boa_engine 0.16.0

//! This module implements the global `String` object.
//!
//! The `String` global object is a constructor for strings or a sequence of characters.
//!
//! More information:
//!  - [ECMAScript reference][spec]
//!  - [MDN documentation][mdn]
//!
//! [spec]: https://tc39.es/ecma262/#sec-string-object
//! [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String

pub mod string_iterator;
#[cfg(test)]
mod tests;

use super::JsArgs;
use crate::{
    builtins::{string::string_iterator::StringIterator, Array, BuiltIn, Number, RegExp},
    context::intrinsics::StandardConstructors,
    object::{
        internal_methods::get_prototype_from_constructor, ConstructorBuilder, JsObject, ObjectData,
    },
    property::{Attribute, PropertyDescriptor},
    symbol::WellKnownSymbols,
    value::IntegerOrInfinity,
    Context, JsResult, JsString, JsValue,
};
use boa_profiler::Profiler;
use std::{
    char::from_u32,
    cmp::{max, min},
    string::String as StdString,
};
use tap::{Conv, Pipe};
use unicode_normalization::UnicodeNormalization;

#[derive(Clone, Copy, Eq, PartialEq)]
pub(crate) enum Placement {
    Start,
    End,
}

/// Code point information for the `CodePointAt` abstract operation.
#[derive(Debug, Clone, Copy)]
pub(crate) struct CodePointInfo {
    pub(crate) code_point: u32,
    pub(crate) code_unit_count: u8,
    pub(crate) is_unpaired_surrogate: bool,
}

/// The `CodePointAt ( string, position )` abstract operation.
///
/// The abstract operation `CodePointAt` takes arguments `string` (a String) and `position` (a
/// non-negative integer) and returns a Record with fields `[[CodePoint]]` (a code point),
/// `[[CodeUnitCount]]` (a positive integer), and `[[IsUnpairedSurrogate]]` (a Boolean). It
/// interprets string as a sequence of UTF-16 encoded code points, as described in 6.1.4, and reads
/// from it a single code point starting with the code unit at index `position`.
///
/// More information:
///  - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-codepointat
pub(crate) fn code_point_at(string: &JsString, position: u64) -> CodePointInfo {
    let mut encoded = string.encode_utf16();

    // 1. Let size be the length of string.
    let size = encoded.clone().count() as u64;

    // 2. Assert: position ≥ 0 and position < size.
    assert!(position < size);

    // 3. Let first be the code unit at index position within string.
    let first = encoded
        .nth(position as usize)
        .expect("The callers of this function must've already checked bounds.");

    // 4. Let cp be the code point whose numeric value is that of first.
    let cp = u32::from(first);

    // 5. If first is not a leading surrogate or trailing surrogate, then
    if !is_leading_surrogate(first) && !is_trailing_surrogate(first) {
        // a. Return the Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]: false }.
        return CodePointInfo {
            code_point: cp,
            code_unit_count: 1,
            is_unpaired_surrogate: false,
        };
    }

    // 6. If first is a trailing surrogate or position + 1 = size, then
    if is_trailing_surrogate(first) || position + 1 == size {
        // a. Return the Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]: true }.
        return CodePointInfo {
            code_point: cp,
            code_unit_count: 1,
            is_unpaired_surrogate: true,
        };
    }

    // 7. Let second be the code unit at index position + 1 within string.
    let second = encoded
        .next()
        .expect("The callers of this function must've already checked bounds.");

    // 8. If second is not a trailing surrogate, then
    if !is_trailing_surrogate(second) {
        // a. Return the Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]: true }.
        return CodePointInfo {
            code_point: cp,
            code_unit_count: 1,
            is_unpaired_surrogate: true,
        };
    }

    // 9. Set cp to UTF16SurrogatePairToCodePoint(first, second).
    let cp = (u32::from(first) - 0xD800) * 0x400 + (u32::from(second) - 0xDC00) + 0x10000;

    // 10. Return the Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 2, [[IsUnpairedSurrogate]]: false }.
    CodePointInfo {
        code_point: cp,
        code_unit_count: 2,
        is_unpaired_surrogate: false,
    }
}

/// Helper function to check if a `char` is trimmable.
#[inline]
pub(crate) fn is_trimmable_whitespace(c: char) -> bool {
    // The rust implementation of `trim` does not regard the same characters whitespace as ecma standard does
    //
    // Rust uses \p{White_Space} by default, which also includes:
    // `\u{0085}' (next line)
    // And does not include:
    // '\u{FEFF}' (zero width non-breaking space)
    // Explicit whitespace: https://tc39.es/ecma262/#sec-white-space
    matches!(
        c,
        '\u{0009}' | '\u{000B}' | '\u{000C}' | '\u{0020}' | '\u{00A0}' | '\u{FEFF}' |
    // Unicode Space_Separator category
    '\u{1680}' | '\u{2000}'
            ..='\u{200A}' | '\u{202F}' | '\u{205F}' | '\u{3000}' |
    // Line terminators: https://tc39.es/ecma262/#sec-line-terminators
    '\u{000A}' | '\u{000D}' | '\u{2028}' | '\u{2029}'
    )
}

/// Checks if the given code unit is a leading surrogate.
///
/// More information:
///  - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#leading-surrogate
pub(crate) fn is_leading_surrogate(value: u16) -> bool {
    (0xD800..=0xDBFF).contains(&value)
}

/// Checks if the given code unit is a trailing surrogate.
///
/// More information:
///  - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#trailing-surrogate
pub(crate) fn is_trailing_surrogate(value: u16) -> bool {
    (0xDC00..=0xDFFF).contains(&value)
}

/// JavaScript `String` implementation.
#[derive(Debug, Clone, Copy)]
pub(crate) struct String;

impl BuiltIn for String {
    const NAME: &'static str = "String";

    fn init(context: &mut Context) -> Option<JsValue> {
        let _timer = Profiler::global().start_event(Self::NAME, "init");

        let symbol_iterator = WellKnownSymbols::iterator();

        let attribute = Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::PERMANENT;
        ConstructorBuilder::with_standard_constructor(
            context,
            Self::constructor,
            context.intrinsics().constructors().string().clone(),
        )
        .name(Self::NAME)
        .length(Self::LENGTH)
        .property("length", 0, attribute)
        .static_method(Self::raw, "raw", 1)
        .static_method(Self::from_char_code, "fromCharCode", 1)
        .static_method(Self::from_code_point, "fromCodePoint", 1)
        .method(Self::char_at, "charAt", 1)
        .method(Self::char_code_at, "charCodeAt", 1)
        .method(Self::code_point_at, "codePointAt", 1)
        .method(Self::to_string, "toString", 0)
        .method(Self::concat, "concat", 1)
        .method(Self::repeat, "repeat", 1)
        .method(Self::slice, "slice", 2)
        .method(Self::starts_with, "startsWith", 1)
        .method(Self::ends_with, "endsWith", 1)
        .method(Self::includes, "includes", 1)
        .method(Self::index_of, "indexOf", 1)
        .method(Self::last_index_of, "lastIndexOf", 1)
        .method(Self::r#match, "match", 1)
        .method(Self::normalize, "normalize", 1)
        .method(Self::pad_end, "padEnd", 1)
        .method(Self::pad_start, "padStart", 1)
        .method(Self::trim, "trim", 0)
        .method(Self::trim_start, "trimStart", 0)
        .method(Self::trim_end, "trimEnd", 0)
        .method(Self::to_lowercase, "toLowerCase", 0)
        .method(Self::to_uppercase, "toUpperCase", 0)
        .method(Self::substring, "substring", 2)
        .method(Self::substr, "substr", 2)
        .method(Self::split, "split", 2)
        .method(Self::value_of, "valueOf", 0)
        .method(Self::match_all, "matchAll", 1)
        .method(Self::replace, "replace", 2)
        .method(Self::replace_all, "replaceAll", 2)
        .method(Self::iterator, (symbol_iterator, "[Symbol.iterator]"), 0)
        .method(Self::search, "search", 1)
        .method(Self::at, "at", 1)
        .build()
        .conv::<JsValue>()
        .pipe(Some)
    }
}

impl String {
    /// The amount of arguments this function object takes.
    pub(crate) const LENGTH: usize = 1;

    /// JavaScript strings must be between `0` and less than positive `Infinity` and cannot be a negative number.
    /// The range of allowed values can be described like this: `[0, +∞)`.
    ///
    /// The resulting string can also not be larger than the maximum string size,
    /// which can differ in JavaScript engines. In Boa it is `2^32 - 1`
    pub(crate) const MAX_STRING_LENGTH: usize = u32::MAX as usize;

    /// `String( value )`
    ///
    /// <https://tc39.es/ecma262/#sec-string-constructor-string-value>
    pub(crate) fn constructor(
        new_target: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // This value is used by console.log and other routines to match Object type
        // to its Javascript Identifier (global constructor method name)
        let string = match args.get(0) {
            // 2. Else,
            // a. If NewTarget is undefined and Type(value) is Symbol, return SymbolDescriptiveString(value).
            Some(JsValue::Symbol(ref sym)) if new_target.is_undefined() => {
                return Ok(sym.descriptive_string().into())
            }
            // b. Let s be ? ToString(value).
            Some(value) => value.to_string(context)?,
            // 1. If value is not present, let s be the empty String.
            None => JsString::default(),
        };

        // 3. If NewTarget is undefined, return s.
        if new_target.is_undefined() {
            return Ok(string.into());
        }

        let prototype =
            get_prototype_from_constructor(new_target, StandardConstructors::string, context)?;
        Ok(Self::string_create(string, prototype, context).into())
    }

    /// Abstract function `StringCreate( value, prototype )`.
    ///
    /// Call this function if you want to create a `String` exotic object.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-stringcreate
    fn string_create(value: JsString, prototype: JsObject, context: &mut Context) -> JsObject {
        // 7. Let length be the number of code unit elements in value.
        let len = value.encode_utf16().count();

        // 1. Let S be ! MakeBasicObject(« [[Prototype]], [[Extensible]], [[StringData]] »).
        // 2. Set S.[[Prototype]] to prototype.
        // 3. Set S.[[StringData]] to value.
        // 4. Set S.[[GetOwnProperty]] as specified in 10.4.3.1.
        // 5. Set S.[[DefineOwnProperty]] as specified in 10.4.3.2.
        // 6. Set S.[[OwnPropertyKeys]] as specified in 10.4.3.3.
        let s = JsObject::from_proto_and_data(prototype, ObjectData::string(value));

        // 8. Perform ! DefinePropertyOrThrow(S, "length", PropertyDescriptor { [[Value]]: 𝔽(length),
        // [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }).
        s.define_property_or_throw(
            "length",
            PropertyDescriptor::builder()
                .value(len)
                .writable(false)
                .enumerable(false)
                .configurable(false),
            context,
        )
        .expect("length definition for a new string must not fail");

        // 9. Return S.
        s
    }

    /// Abstract operation `thisStringValue( value )`
    ///
    /// More information:
    /// - [ECMAScript reference][spec]
    ///
    /// [spec]: https://tc39.es/ecma262/#thisstringvalue
    fn this_string_value(this: &JsValue, context: &mut Context) -> JsResult<JsString> {
        // 1. If Type(value) is String, return value.
        this.as_string()
            .cloned()
            // 2. If Type(value) is Object and value has a [[StringData]] internal slot, then
            //     a. Let s be value.[[StringData]].
            //     b. Assert: Type(s) is String.
            //     c. Return s.
            .or_else(|| this.as_object().and_then(|obj| obj.borrow().as_string()))
            // 3. Throw a TypeError exception.
            .ok_or_else(|| context.construct_type_error("'this' is not a string"))
    }

    /// `String.fromCodePoint(num1[, ...[, numN]])`
    ///
    /// The static `String.fromCodePoint()` method returns a string created by using the specified sequence of code points.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.fromcodepoint
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/fromCodePoint
    pub(crate) fn from_code_point(
        _: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let result be the empty String.
        let mut result = StdString::new();

        // 2. For each element next of codePoints, do
        for arg in args.iter() {
            // a. Let nextCP be ? ToNumber(next).
            let nextcp = arg.to_number(context)?;

            // b. If ! IsIntegralNumber(nextCP) is false, throw a RangeError exception.
            if !Number::is_float_integer(nextcp) {
                return Err(context.construct_range_error(format!("invalid code point: {nextcp}")));
            }

            // c. If ℝ(nextCP) < 0 or ℝ(nextCP) > 0x10FFFF, throw a RangeError exception.
            if nextcp < 0.0 || nextcp > f64::from(0x10FFFF) {
                return Err(context.construct_range_error(format!("invalid code point: {nextcp}")));
            }

            // TODO: Full UTF-16 support
            // d. Set result to the string-concatenation of result and ! UTF16EncodeCodePoint(ℝ(nextCP)).
            result.push(char::try_from(nextcp as u32).unwrap_or('\u{FFFD}' /* replacement char */));
        }

        // 3. Assert: If codePoints is empty, then result is the empty String.
        // 4. Return result.
        Ok(result.into())
    }

    /// `String.prototype.raw( template, ...substitutions )`
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.raw
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/raw
    pub(crate) fn raw(_: &JsValue, args: &[JsValue], context: &mut Context) -> JsResult<JsValue> {
        let substitutions = args.get(1..).unwrap_or_default();

        // 1. Let numberOfSubstitutions be the number of elements in substitutions.
        let number_of_substitutions = substitutions.len() as u64;

        // 2. Let cooked be ? ToObject(template).
        let cooked = args.get_or_undefined(0).to_object(context)?;

        // 3. Let raw be ? ToObject(? Get(cooked, "raw")).
        let raw = cooked.get("raw", context)?.to_object(context)?;

        // 4. Let literalSegments be ? LengthOfArrayLike(raw).
        let literal_segments = raw.length_of_array_like(context)?;

        // 5. If literalSegments ≤ 0, return the empty String.
        // This is not <= because a `usize` is always positive.
        if literal_segments == 0 {
            return Ok(JsString::empty().into());
        }

        // 6. Let stringElements be a new empty List.
        let mut string_elements = vec![];

        // 7. Let nextIndex be 0.
        let mut next_index = 0;
        // 8. Repeat,
        loop {
            // a. Let nextKey be ! ToString(𝔽(nextIndex)).
            let next_key = next_index;

            // b. Let nextSeg be ? ToString(? Get(raw, nextKey)).
            let next_seg = raw.get(next_key, context)?.to_string(context)?;

            // c. Append the code unit elements of nextSeg to the end of stringElements.
            string_elements.extend(next_seg.encode_utf16());

            // d. If nextIndex + 1 = literalSegments, then
            if next_index + 1 == literal_segments {
                // i. Return the String value whose code units are the elements in the List stringElements.
                //    If stringElements has no elements, the empty String is returned.
                return Ok(StdString::from_utf16_lossy(&string_elements).into());
            }

            // e. If nextIndex < numberOfSubstitutions, let next be substitutions[nextIndex].
            let next = if next_index < number_of_substitutions {
                substitutions.get_or_undefined(next_index as usize).clone()

            // f. Else, let next be the empty String.
            } else {
                JsString::empty().into()
            };

            // g. Let nextSub be ? ToString(next).
            let next_sub = next.to_string(context)?;

            // h. Append the code unit elements of nextSub to the end of stringElements.
            string_elements.extend(next_sub.encode_utf16());

            // i. Set nextIndex to nextIndex + 1.
            next_index += 1;
        }
    }

    /// `String.fromCharCode(...codeUnits)`
    ///
    /// Construct a `String` from one or more code points (as numbers).
    /// More information:
    /// - [ECMAScript reference][spec]
    ///
    /// [spec]: https://tc39.es/ecma262/multipage/text-processing.html#sec-string.fromcharcode
    pub(crate) fn from_char_code(
        _: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let result be the empty String.
        let mut result = Vec::new();

        // 2. For each element next of codeUnits, do
        for next in args {
            // a. Let nextCU be the code unit whose numeric value is ℝ(? ToUint16(next)).
            let next_cu = next.to_uint16(context)?;

            // b. Set result to the string-concatenation of result and nextCU.
            result.push(next_cu);
        }

        // 3. Return result.
        Ok(JsValue::String(JsString::new(
            std::string::String::from_utf16_lossy(&result),
        )))
    }

    /// `String.prototype.toString ( )`
    ///
    /// More information:
    /// - [ECMAScript reference][spec]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.tostring
    #[allow(clippy::wrong_self_convention)]
    #[inline]
    pub(crate) fn to_string(
        this: &JsValue,
        _: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Return ? thisStringValue(this value).
        Ok(Self::this_string_value(this, context)?.into())
    }

    /// `String.prototype.charAt( index )`
    ///
    /// The `String` object's `charAt()` method returns a new string consisting of the single UTF-16 code unit located at the specified offset into the string.
    ///
    /// Characters in a string are indexed from left to right. The index of the first character is `0`,
    /// and the index of the last character—in a string called `stringName`—is `stringName.length - 1`.
    /// If the `index` you supply is out of this range, JavaScript returns an empty string.
    ///
    /// If no index is provided to `charAt()`, the default is `0`.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.charat
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/charAt
    pub(crate) fn char_at(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        // 4. Let size be the length of S.
        let size = string.encode_utf16().count() as i64;

        // 3. Let position be ? ToIntegerOrInfinity(pos).
        match args.get_or_undefined(0).to_integer_or_infinity(context)? {
            IntegerOrInfinity::Integer(position) if (0..size).contains(&position) => {
                // 6. Return the substring of S from position to position + 1.
                let char = string
                    .encode_utf16()
                    .nth(position as usize)
                    .expect("Already checked bounds above");

                Ok(char::try_from(u32::from(char))
                    .unwrap_or('\u{FFFD}' /* replacement char */)
                    .into())
            }
            _ => {
                // 5. If position < 0 or position ≥ size, return the empty String.
                Ok("".into())
            }
        }
    }

    /// `String.prototype.at ( index )`
    ///
    /// This String object's at() method returns a String consisting of the single UTF-16 code unit located at the specified position.
    /// Returns undefined if the given index cannot be found.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/proposal-relative-indexing-method/#sec-string.prototype.at
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/at
    pub(crate) fn at(this: &JsValue, args: &[JsValue], context: &mut Context) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let s = this.to_string(context)?;

        // 3. Let len be the length of S.
        let len = s.encode_utf16().count() as i64;

        // 4. Let relativeIndex be ? ToIntegerOrInfinity(index).
        let relative_index = args.get_or_undefined(0).to_integer_or_infinity(context)?;
        let k = match relative_index {
            // 5. If relativeIndex ≥ 0, then
            // a. Let k be relativeIndex.
            IntegerOrInfinity::Integer(i) if i >= 0 && i < len => i as usize,
            // 6. Else,
            // a. Let k be len + relativeIndex.
            IntegerOrInfinity::Integer(i) if i < 0 && (-i) <= len => (len + i) as usize,
            // 7. If k < 0 or k ≥ len, return undefined.
            _ => return Ok(JsValue::undefined()),
        };

        // 8. Return the substring of S from k to k + 1.
        if let Some(utf16_val) = s.encode_utf16().nth(k) {
            Ok(JsValue::new(
                from_u32(u32::from(utf16_val)).expect("invalid utf-16 character"),
            ))
        } else {
            Ok(JsValue::undefined())
        }
    }

    /// `String.prototype.codePointAt( index )`
    ///
    /// The `codePointAt()` method returns an integer between `0` to `1114111` (`0x10FFFF`) representing the UTF-16 code unit at the given index.
    ///
    /// If no UTF-16 surrogate pair begins at the index, the code point at the index is returned.
    ///
    /// `codePointAt()` returns `undefined` if the given index is less than `0`, or if it is equal to or greater than the `length` of the string.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.codepointat
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/codePointAt
    pub(crate) fn code_point_at(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        // 3. Let position be ? ToIntegerOrInfinity(pos).
        let position = args.get_or_undefined(0).to_integer_or_infinity(context)?;

        // 4. Let size be the length of S.
        let size = string.encode_utf16().count() as i64;

        match position {
            IntegerOrInfinity::Integer(position) if (0..size).contains(&position) => {
                // 6. Let cp be ! CodePointAt(S, position).
                // 7. Return 𝔽(cp.[[CodePoint]]).
                Ok(code_point_at(&string, position as u64).code_point.into())
            }
            // 5. If position < 0 or position ≥ size, return undefined.
            _ => Ok(JsValue::undefined()),
        }
    }

    /// `String.prototype.charCodeAt( index )`
    ///
    /// The `charCodeAt()` method returns an integer between `0` and `65535` representing the UTF-16 code unit at the given index.
    ///
    /// Unicode code points range from `0` to `1114111` (`0x10FFFF`). The first 128 Unicode code points are a direct match of the ASCII character encoding.
    ///
    /// `charCodeAt()` returns `NaN` if the given index is less than `0`, or if it is equal to or greater than the `length` of the string.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.charcodeat
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/charCodeAt
    pub(crate) fn char_code_at(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        // 3. Let position be ? ToIntegerOrInfinity(pos).
        let position = args.get_or_undefined(0).to_integer_or_infinity(context)?;

        // 4. Let size be the length of S.
        let size = string.encode_utf16().count() as i64;

        match position {
            IntegerOrInfinity::Integer(position) if (0..size).contains(&position) => {
                // 6. Return the Number value for the numeric value of the code unit at index position within the String S.
                let char_code = u32::from(
                    string
                        .encode_utf16()
                        .nth(position as usize)
                        .expect("Already checked bounds above."),
                );
                Ok(char_code.into())
            }
            // 5. If position < 0 or position ≥ size, return NaN.
            _ => Ok(JsValue::nan()),
        }
    }

    /// `String.prototype.concat( str1[, ...strN] )`
    ///
    /// The `concat()` method concatenates the string arguments to the calling string and returns a new string.
    ///
    /// Changes to the original string or the returned string don't affect the other.
    ///
    /// If the arguments are not of the type string, they are converted to string values before concatenating.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.concat
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/concat
    pub(crate) fn concat(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let mut string = this.to_string(context)?.to_string();

        // 3. Let R be S.
        // 4. For each element next of args, do
        for arg in args {
            // a. Let nextString be ? ToString(next).
            // b. Set R to the string-concatenation of R and nextString.
            string.push_str(&arg.to_string(context)?);
        }

        // 5. Return R.
        Ok(JsValue::new(string))
    }

    /// `String.prototype.repeat( count )`
    ///
    /// The `repeat()` method constructs and returns a new string which contains the specified number of
    /// copies of the string on which it was called, concatenated together.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.repeat
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/repeat
    pub(crate) fn repeat(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        let len = string.encode_utf16().count();

        // 3. Let n be ? ToIntegerOrInfinity(count).
        match args.get_or_undefined(0).to_integer_or_infinity(context)? {
            IntegerOrInfinity::Integer(n)
                if n > 0 && (n as usize) * len <= Self::MAX_STRING_LENGTH =>
            {
                if string.is_empty() {
                    return Ok("".into());
                }
                let n = n as usize;
                let mut result = std::string::String::with_capacity(n * len);

                std::iter::repeat(&string[..])
                    .take(n)
                    .for_each(|s| result.push_str(s));

                // 6. Return the String value that is made from n copies of S appended together.
                Ok(result.into())
            }
            // 5. If n is 0, return the empty String.
            IntegerOrInfinity::Integer(n) if n == 0 => Ok("".into()),
            // 4. If n < 0 or n is +∞, throw a RangeError exception.
            _ => context.throw_range_error(
                "repeat count must be a positive finite number \
                        that doesn't overflow the maximum string length (2^32 - 1)",
            ),
        }
    }

    /// `String.prototype.slice( beginIndex [, endIndex] )`
    ///
    /// The `slice()` method extracts a section of a string and returns it as a new string, without modifying the original string.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.slice
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice
    pub(crate) fn slice(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        // 3. Let len be the length of S.
        let len = string.encode_utf16().count() as i64;

        // 4. Let intStart be ? ToIntegerOrInfinity(start).
        let from = match args.get_or_undefined(0).to_integer_or_infinity(context)? {
            // 6. Else if intStart < 0, let from be max(len + intStart, 0).
            IntegerOrInfinity::Integer(i) if i < 0 => max(len + i, 0),

            // 7. Else, let from be min(intStart, len).
            IntegerOrInfinity::Integer(i) => min(i, len),
            IntegerOrInfinity::PositiveInfinity => len,

            // 5. If intStart is -∞, let from be 0.
            IntegerOrInfinity::NegativeInfinity => 0,
        } as usize;

        // 8. If end is undefined, let intEnd be len; else let intEnd be ? ToIntegerOrInfinity(end).
        let to = match args
            .get(1)
            .filter(|end| !end.is_undefined())
            .map(|end| end.to_integer_or_infinity(context))
            .transpose()?
            .unwrap_or(IntegerOrInfinity::Integer(len))
        {
            // 10. Else if intEnd < 0, let to be max(len + intEnd, 0).
            IntegerOrInfinity::Integer(i) if i < 0 => max(len + i, 0),

            // 11. Else, let to be min(intEnd, len).
            IntegerOrInfinity::Integer(i) => min(i, len),
            IntegerOrInfinity::PositiveInfinity => len,

            // 9. If intEnd is -∞, let to be 0.
            IntegerOrInfinity::NegativeInfinity => 0,
        } as usize;

        // 12. If from ≥ to, return the empty String.
        if from >= to {
            Ok("".into())
        } else {
            // 13. Return the substring of S from from to to.
            let span = to - from;
            let substring_utf16: Vec<u16> = string.encode_utf16().skip(from).take(span).collect();
            let substring_lossy = StdString::from_utf16_lossy(&substring_utf16);
            Ok(substring_lossy.into())
        }
    }

    /// `String.prototype.startWith( searchString[, position] )`
    ///
    /// The `startsWith()` method determines whether a string begins with the characters of a specified string, returning `true` or `false` as appropriate.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.startswith
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/startsWith
    pub(crate) fn starts_with(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        let search_string = args.get_or_undefined(0);

        // 3. Let isRegExp be ? IsRegExp(searchString).
        // 4. If isRegExp is true, throw a TypeError exception.
        if is_reg_exp(search_string, context)? {
            context.throw_type_error(
                "First argument to String.prototype.startsWith must not be a regular expression",
            )?;
        }

        // 5. Let searchStr be ? ToString(searchString).
        let search_string = search_string.to_string(context)?;

        // 6. Let len be the length of S.
        let len = string.encode_utf16().count() as i64;

        // 7. If position is undefined, let pos be 0; else let pos be ? ToIntegerOrInfinity(position).
        let pos = match args.get_or_undefined(1) {
            &JsValue::Undefined => IntegerOrInfinity::Integer(0),
            position => position.to_integer_or_infinity(context)?,
        };

        // 8. Let start be the result of clamping pos between 0 and len.
        let start = pos.clamp_finite(0, len) as usize;

        // 9. Let searchLength be the length of searchStr.
        let search_length = search_string.encode_utf16().count();

        // 10. If searchLength = 0, return true.
        if search_length == 0 {
            return Ok(JsValue::new(true));
        }

        // 11. Let end be start + searchLength.
        let end = start + search_length;

        // 12. If end > len, return false.
        if end > len as usize {
            Ok(JsValue::new(false))
        } else {
            // 13. Let substring be the substring of S from start to end.
            // 14. Return ! SameValueNonNumeric(substring, searchStr).
            // `SameValueNonNumeric` forwards to `==`, so directly check
            // equality to avoid converting to `JsValue`
            let substring_utf16 = string.encode_utf16().skip(start).take(search_length);
            let search_str_utf16 = search_string.encode_utf16();
            Ok(JsValue::new(substring_utf16.eq(search_str_utf16)))
        }
    }

    /// `String.prototype.endsWith( searchString[, length] )`
    ///
    /// The `endsWith()` method determines whether a string ends with the characters of a specified string, returning `true` or `false` as appropriate.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.endswith
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/endsWith
    pub(crate) fn ends_with(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        let search_str = match args.get_or_undefined(0) {
            // 3. Let isRegExp be ? IsRegExp(searchString).
            // 4. If isRegExp is true, throw a TypeError exception.
            search_string if is_reg_exp(search_string, context)? => {
                return context.throw_type_error(
                    "First argument to String.prototype.endsWith must not be a regular expression",
                );
            }
            // 5. Let searchStr be ? ToString(searchString).
            search_string => search_string.to_string(context)?,
        };

        // 6. Let len be the length of S.
        let len = string.encode_utf16().count() as i64;

        // 7. If endPosition is undefined, let pos be len; else let pos be ? ToIntegerOrInfinity(endPosition).
        let end = match args.get_or_undefined(1) {
            end_position if end_position.is_undefined() => IntegerOrInfinity::Integer(len),
            end_position => end_position.to_integer_or_infinity(context)?,
        };

        // 8. Let end be the result of clamping pos between 0 and len.
        let end = end.clamp_finite(0, len) as usize;

        // 9. Let searchLength be the length of searchStr.
        let search_length = search_str.encode_utf16().count();

        // 10. If searchLength = 0, return true.
        if search_length == 0 {
            return Ok(true.into());
        }

        // 11. Let start be end - searchLength.
        if let Some(start) = end.checked_sub(search_length) {
            // 13. Let substring be the substring of S from start to end.
            // 14. Return ! SameValueNonNumeric(substring, searchStr).
            // `SameValueNonNumeric` forwards to `==`, so directly check
            // equality to avoid converting to `JsValue`

            let substring_utf16 = string.encode_utf16().skip(start).take(search_length);
            let search_str_utf16 = search_str.encode_utf16();

            Ok(JsValue::new(substring_utf16.eq(search_str_utf16)))
        } else {
            // 12. If start < 0, return false.
            Ok(false.into())
        }
    }

    /// `String.prototype.includes( searchString[, position] )`
    ///
    /// The `includes()` method determines whether one string may be found within another string, returning `true` or `false` as appropriate.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.includes
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/includes
    pub(crate) fn includes(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        let search_str = match args.get_or_undefined(0) {
            // 3. Let isRegExp be ? IsRegExp(searchString).
            search_string if is_reg_exp(search_string, context)? => {
                return context.throw_type_error(
                    // 4. If isRegExp is true, throw a TypeError exception.
                    "First argument to String.prototype.includes must not be a regular expression",
                );
            }
            // 5. Let searchStr be ? ToString(searchString).
            search_string => search_string.to_string(context)?,
        };

        // 6. Let pos be ? ToIntegerOrInfinity(position).
        // 7. Assert: If position is undefined, then pos is 0.
        let pos = args.get_or_undefined(1).to_integer_or_infinity(context)?;

        // 8. Let len be the length of S.
        // 9. Let start be the result of clamping pos between 0 and len.
        let start = pos.clamp_finite(0, string.encode_utf16().count() as i64) as usize;

        // 10. Let index be ! StringIndexOf(S, searchStr, start).
        // 11. If index is not -1, return true.
        // 12. Return false.
        Ok(string.index_of(&search_str, start).is_some().into())
    }

    /// `String.prototype.replace( regexp|substr, newSubstr|function )`
    ///
    /// The `replace()` method returns a new string with some or all matches of a `pattern` replaced by a `replacement`.
    ///
    /// The `pattern` can be a string or a `RegExp`, and the `replacement` can be a string or a function to be called for each match.
    /// If `pattern` is a string, only the first occurrence will be replaced.
    ///
    /// The original string is left unchanged.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.replace
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace
    pub(crate) fn replace(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        this.require_object_coercible(context)?;

        let search_value = args.get_or_undefined(0);

        let replace_value = args.get_or_undefined(1);

        // 2. If searchValue is neither undefined nor null, then
        if !search_value.is_null_or_undefined() {
            // a. Let replacer be ? GetMethod(searchValue, @@replace).
            let replacer = search_value.get_method(WellKnownSymbols::replace(), context)?;

            // b. If replacer is not undefined, then
            if let Some(replacer) = replacer {
                // i. Return ? Call(replacer, searchValue, « O, replaceValue »).
                return replacer.call(
                    search_value,
                    &[this.clone(), replace_value.clone()],
                    context,
                );
            }
        }

        // 3. Let string be ? ToString(O).
        let this_str = this.to_string(context)?;

        // 4. Let searchString be ? ToString(searchValue).
        let search_str = search_value.to_string(context)?;

        // 5. Let functionalReplace be IsCallable(replaceValue).
        let functional_replace = replace_value
            .as_object()
            .map(JsObject::is_callable)
            .unwrap_or_default();

        // 6. If functionalReplace is false, then
        // a. Set replaceValue to ? ToString(replaceValue).

        // 7. Let searchLength be the length of searchString.
        let search_length = search_str.len();

        // 8. Let position be ! StringIndexOf(string, searchString, 0).
        // 9. If position is -1, return string.
        let position = if let Some(p) = this_str.index_of(&search_str, 0) {
            p
        } else {
            return Ok(this_str.into());
        };

        // 10. Let preserved be the substring of string from 0 to position.
        let preserved = StdString::from_utf16_lossy(
            &this_str.encode_utf16().take(position).collect::<Vec<u16>>(),
        );

        // 11. If functionalReplace is true, then
        // 12. Else,
        let replacement = if functional_replace {
            // a. Let replacement be ? ToString(? Call(replaceValue, undefined, « searchString, 𝔽(position), string »)).
            context
                .call(
                    replace_value,
                    &JsValue::undefined(),
                    &[search_str.into(), position.into(), this_str.clone().into()],
                )?
                .to_string(context)?
        } else {
            // a. Assert: Type(replaceValue) is String.
            // b. Let captures be a new empty List.
            let captures = Vec::new();

            // c. Let replacement be ! GetSubstitution(searchString, string, position, captures, undefined, replaceValue).
            get_substitution(
                search_str.as_str(),
                this_str.as_str(),
                position,
                &captures,
                &JsValue::undefined(),
                &replace_value.to_string(context)?,
                context,
            )?
        };

        // 13. Return the string-concatenation of preserved, replacement, and the substring of string from position + searchLength.
        Ok(format!(
            "{preserved}{replacement}{}",
            StdString::from_utf16_lossy(
                &this_str
                    .encode_utf16()
                    .skip(position + search_length)
                    .collect::<Vec<u16>>()
            )
        )
        .into())
    }

    /// `22.1.3.18 String.prototype.replaceAll ( searchValue, replaceValue )`
    ///
    /// The replaceAll() method returns a new string with all matches of a pattern replaced by a
    /// replacement.
    ///
    /// The pattern can be a string or a `RegExp`, and the replacement can be a string or a
    /// function to be called for each match.
    ///
    /// The original string is left unchanged.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.replaceall
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace
    pub(crate) fn replace_all(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let o = this.require_object_coercible(context)?;

        let search_value = args.get_or_undefined(0);
        let replace_value = args.get_or_undefined(1);

        // 2. If searchValue is neither undefined nor null, then
        if !search_value.is_null_or_undefined() {
            // a. Let isRegExp be ? IsRegExp(searchValue).
            if let Some(obj) = search_value.as_object() {
                // b. If isRegExp is true, then
                if is_reg_exp_object(obj, context)? {
                    // i. Let flags be ? Get(searchValue, "flags").
                    let flags = obj.get("flags", context)?;

                    // ii. Perform ? RequireObjectCoercible(flags).
                    flags.require_object_coercible(context)?;

                    // iii. If ? ToString(flags) does not contain "g", throw a TypeError exception.
                    if !flags.to_string(context)?.contains('g') {
                        return context.throw_type_error(
                            "String.prototype.replaceAll called with a non-global RegExp argument",
                        );
                    }
                }
            }

            // c. Let replacer be ? GetMethod(searchValue, @@replace).
            let replacer = search_value.get_method(WellKnownSymbols::replace(), context)?;

            // d. If replacer is not undefined, then
            if let Some(replacer) = replacer {
                // i. Return ? Call(replacer, searchValue, « O, replaceValue »).
                return replacer.call(search_value, &[o.into(), replace_value.clone()], context);
            }
        }

        // 3. Let string be ? ToString(O).
        let string = o.to_string(context)?;

        // 4. Let searchString be ? ToString(searchValue).
        let search_string = search_value.to_string(context)?;

        // 5. Let functionalReplace be IsCallable(replaceValue).
        let functional_replace = replace_value
            .as_object()
            .map(JsObject::is_callable)
            .unwrap_or_default();

        let replace_value_string = if functional_replace {
            None
        } else {
            // a. Set replaceValue to ? ToString(replaceValue).
            // 6. If functionalReplace is false, then
            Some(replace_value.to_string(context)?)
        };

        // 7. Let searchLength be the length of searchString.
        let search_length = search_string.encode_utf16().count();

        // 8. Let advanceBy be max(1, searchLength).
        let advance_by = max(1, search_length);

        // 9. Let matchPositions be a new empty List.
        let mut match_positions = Vec::new();

        // 10. Let position be ! StringIndexOf(string, searchString, 0).
        let mut position = string.index_of(&search_string, 0);

        // 11. Repeat, while position is not -1,
        while let Some(p) = position {
            // a. Append position to the end of matchPositions.
            match_positions.push(p);

            // b. Set position to ! StringIndexOf(string, searchString, position + advanceBy).
            position = string.index_of(&search_string, p + advance_by);
        }

        // 12. Let endOfLastMatch be 0.
        let mut end_of_last_match = 0;

        // 13. Let result be the empty String.
        let mut result = JsString::new("");

        // 14. For each element p of matchPositions, do
        for p in match_positions {
            // a. Let preserved be the substring of string from endOfLastMatch to p.
            let preserved = StdString::from_utf16_lossy(
                &string
                    .clone()
                    .encode_utf16()
                    .skip(end_of_last_match)
                    .take(p - end_of_last_match)
                    .collect::<Vec<u16>>(),
            );

            // c. Else,
            let replacement = if let Some(ref replace_value) = replace_value_string {
                // i. Assert: Type(replaceValue) is String.
                // ii. Let captures be a new empty List.
                // iii. Let replacement be ! GetSubstitution(searchString, string, p, captures, undefined, replaceValue).
                get_substitution(
                    &search_string,
                    &string,
                    p,
                    &[],
                    &JsValue::undefined(),
                    replace_value,
                    context,
                )
                .expect("GetSubstitution should never fail here.")
            }
            // b. If functionalReplace is true, then
            else {
                // i. Let replacement be ? ToString(? Call(replaceValue, undefined, « searchString, 𝔽(p), string »)).
                context
                    .call(
                        replace_value,
                        &JsValue::undefined(),
                        &[
                            search_string.clone().into(),
                            p.into(),
                            string.clone().into(),
                        ],
                    )?
                    .to_string(context)?
            };

            // d. Set result to the string-concatenation of result, preserved, and replacement.
            result = JsString::new(format!("{}{preserved}{replacement}", result.as_str()));

            // e. Set endOfLastMatch to p + searchLength.
            end_of_last_match = p + search_length;
        }

        // 15. If endOfLastMatch < the length of string, then
        if end_of_last_match < string.encode_utf16().count() {
            // a. Set result to the string-concatenation of result and the substring of string from endOfLastMatch.
            result = JsString::new(format!(
                "{}{}",
                result.as_str(),
                &StdString::from_utf16_lossy(
                    &string
                        .encode_utf16()
                        .skip(end_of_last_match)
                        .collect::<Vec<u16>>()
                )
            ));
        }

        // 16. Return result.
        Ok(result.into())
    }

    /// `String.prototype.indexOf( searchValue[, fromIndex] )`
    ///
    /// The `indexOf()` method returns the index within the calling `String` object of the first occurrence
    /// of the specified value, starting the search at `fromIndex`.
    ///
    /// Returns `-1` if the value is not found.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.indexof
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf
    pub(crate) fn index_of(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        // 3. Let searchStr be ? ToString(searchString).
        let search_str = args.get_or_undefined(0).to_string(context)?;

        // 4. Let pos be ? ToIntegerOrInfinity(position).
        // 5. Assert: If position is undefined, then pos is 0.
        let pos = args.get_or_undefined(1).to_integer_or_infinity(context)?;

        // 6. Let len be the length of S.
        let len = string.encode_utf16().count() as i64;

        // 7. Let start be the result of clamping pos between 0 and len.
        let start = pos.clamp_finite(0, len) as usize;

        // 8. Return 𝔽(! StringIndexOf(S, searchStr, start)).
        Ok(string
            .index_of(&search_str, start)
            .map_or(-1, |i| i as i64)
            .into())
    }

    /// `String.prototype.lastIndexOf( searchValue[, fromIndex] )`
    ///
    /// The `lastIndexOf()` method returns the index within the calling `String` object of the last occurrence
    /// of the specified value, searching backwards from `fromIndex`.
    ///
    /// Returns `-1` if the value is not found.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.lastindexof
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/lastIndexOf
    pub(crate) fn last_index_of(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        // 3. Let searchStr be ? ToString(searchString).
        let search_str = args.get_or_undefined(0).to_string(context)?;

        // 4. Let numPos be ? ToNumber(position).
        // 5. Assert: If position is undefined, then numPos is NaN.
        let num_pos = args.get_or_undefined(1).to_number(context)?;

        // 6. If numPos is NaN, let pos be +∞; otherwise, let pos be ! ToIntegerOrInfinity(numPos).
        let pos = if num_pos.is_nan() {
            IntegerOrInfinity::PositiveInfinity
        } else {
            JsValue::new(num_pos)
                .to_integer_or_infinity(context)
                .expect("Already called `to_number so this must not fail.")
        };

        // 7. Let len be the length of S.
        let len = string.encode_utf16().count();
        // 8. Let start be the result of clamping pos between 0 and len.
        let start = pos.clamp_finite(0, len as i64) as usize;

        // 9. If searchStr is the empty String, return 𝔽(start).
        if search_str.is_empty() {
            return Ok(JsValue::new(start));
        }

        // 10. Let searchLen be the length of searchStr.
        let search_len = search_str.encode_utf16().count();

        // 11. For each non-negative integer i starting with start such that i ≤ len - searchLen, in descending order, do
        // a. Let candidate be the substring of S from i to i + searchLen.
        let substring_utf16: Vec<u16> = string.encode_utf16().take(start + search_len).collect();
        let substring_lossy = StdString::from_utf16_lossy(&substring_utf16);
        if let Some(position) = substring_lossy.rfind(search_str.as_str()) {
            // b. If candidate is the same sequence of code units as searchStr, return 𝔽(i).
            return Ok(JsValue::new(
                substring_lossy[..position].encode_utf16().count(),
            ));
        }

        // 12. Return -1𝔽.
        Ok(JsValue::new(-1))
    }

    /// `String.prototype.match( regexp )`
    ///
    /// The `match()` method retrieves the result of matching a **string** against a [`regular expression`][regex].
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.match
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match
    /// [regex]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions
    pub(crate) fn r#match(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let o = this.require_object_coercible(context)?;

        // 2. If regexp is neither undefined nor null, then
        let regexp = args.get_or_undefined(0);
        if !regexp.is_null_or_undefined() {
            // a. Let matcher be ? GetMethod(regexp, @@match).
            let matcher = regexp.get_method(WellKnownSymbols::r#match(), context)?;
            // b. If matcher is not undefined, then
            if let Some(matcher) = matcher {
                // i. Return ? Call(matcher, regexp, « O »).
                return matcher.call(regexp, &[o.clone()], context);
            }
        }

        // 3. Let S be ? ToString(O).
        let s = o.to_string(context)?;

        // 4. Let rx be ? RegExpCreate(regexp, undefined).
        let rx = RegExp::create(regexp, &JsValue::Undefined, context)?;

        // 5. Return ? Invoke(rx, @@match, « S »).
        rx.invoke(WellKnownSymbols::r#match(), &[JsValue::new(s)], context)
    }

    /// Abstract operation `StringPad ( O, maxLength, fillString, placement )`.
    ///
    /// Performs the actual string padding for padStart/End.
    ///
    /// More information:
    /// - [ECMAScript reference][spec]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-stringpad
    fn string_pad(
        object: &JsValue,
        max_length: &JsValue,
        fill_string: &JsValue,
        placement: Placement,
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let S be ? ToString(O).
        let string = object.to_string(context)?;

        // 2. Let intMaxLength be ℝ(? ToLength(maxLength)).
        let int_max_length = max_length.to_length(context)?;

        // 3. Let stringLength be the length of S.
        let string_length = string.encode_utf16().count() as u64;

        // 4. If intMaxLength ≤ stringLength, return S.
        if int_max_length <= string_length {
            return Ok(string.into());
        }

        // 5. If fillString is undefined, let filler be the String value consisting solely of the code unit 0x0020 (SPACE).
        let filler = if fill_string.is_undefined() {
            "\u{0020}".into()
        } else {
            // 6. Else, let filler be ? ToString(fillString).
            fill_string.to_string(context)?
        };

        // 7. If filler is the empty String, return S.
        if filler.is_empty() {
            return Ok(string.into());
        }

        // 8. Let fillLen be intMaxLength - stringLength.
        let fill_len = int_max_length - string_length;
        let filler_len = filler.encode_utf16().count() as u64;

        // 9. Let truncatedStringFiller be the String value consisting of repeated
        // concatenations of filler truncated to length fillLen.
        let repetitions = {
            let q = fill_len / filler_len;
            let r = fill_len % filler_len;
            if r == 0 {
                q
            } else {
                q + 1
            }
        };

        let truncated_string_filler = filler
            .repeat(repetitions as usize)
            .encode_utf16()
            .take(fill_len as usize)
            .collect::<Vec<_>>();
        let truncated_string_filler =
            std::string::String::from_utf16_lossy(truncated_string_filler.as_slice());

        // 10. If placement is start, return the string-concatenation of truncatedStringFiller and S.
        if placement == Placement::Start {
            Ok(format!("{truncated_string_filler}{string}").into())
        } else {
            // 11. Else, return the string-concatenation of S and truncatedStringFiller.
            Ok(format!("{string}{truncated_string_filler}").into())
        }
    }

    /// `String.prototype.padEnd( targetLength[, padString] )`
    ///
    /// The `padEnd()` method pads the current string with a given string (repeated, if needed) so that the resulting string reaches a given length.
    ///
    /// The padding is applied from the end of the current string.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.padend
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padEnd
    pub(crate) fn pad_end(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        let max_length = args.get_or_undefined(0);
        let fill_string = args.get_or_undefined(1);

        // 2. Return ? StringPad(O, maxLength, fillString, end).
        Self::string_pad(this, max_length, fill_string, Placement::End, context)
    }

    /// `String.prototype.padStart( targetLength [, padString] )`
    ///
    /// The `padStart()` method pads the current string with another string (multiple times, if needed) until the resulting string reaches the given length.
    ///
    /// The padding is applied from the start of the current string.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.padstart
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart
    pub(crate) fn pad_start(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        let max_length = args.get_or_undefined(0);
        let fill_string = args.get_or_undefined(1);

        // 2. Return ? StringPad(O, maxLength, fillString, start).
        Self::string_pad(this, max_length, fill_string, Placement::Start, context)
    }

    /// String.prototype.trim()
    ///
    /// The `trim()` method removes whitespace from both ends of a string.
    ///
    /// Whitespace in this context is all the whitespace characters (space, tab, no-break space, etc.) and all the line terminator characters (LF, CR, etc.).
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.trim
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trim
    pub(crate) fn trim(this: &JsValue, _: &[JsValue], context: &mut Context) -> JsResult<JsValue> {
        let object = this.require_object_coercible(context)?;
        let string = object.to_string(context)?;
        Ok(JsValue::new(string.trim_matches(is_trimmable_whitespace)))
    }

    /// `String.prototype.trimStart()`
    ///
    /// The `trimStart()` method removes whitespace from the beginning of a string.
    ///
    /// Whitespace in this context is all the whitespace characters (space, tab, no-break space, etc.) and all the line terminator characters (LF, CR, etc.).
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.trimstart
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trimStart
    pub(crate) fn trim_start(
        this: &JsValue,
        _: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        let this = this.require_object_coercible(context)?;
        let string = this.to_string(context)?;
        Ok(JsValue::new(
            string.trim_start_matches(is_trimmable_whitespace),
        ))
    }

    /// String.prototype.trimEnd()
    ///
    /// The `trimEnd()` method removes whitespace from the end of a string.
    ///
    /// Whitespace in this context is all the whitespace characters (space, tab, no-break space, etc.) and all the line terminator characters (LF, CR, etc.).
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.trimend
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trimEnd
    pub(crate) fn trim_end(
        this: &JsValue,
        _: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        let this = this.require_object_coercible(context)?;
        let string = this.to_string(context)?;
        Ok(JsValue::new(
            string.trim_end_matches(is_trimmable_whitespace),
        ))
    }

    /// `String.prototype.toLowerCase()`
    ///
    /// The `toLowerCase()` method returns the calling string value converted to lower case.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.tolowercase
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toLowerCase
    #[allow(clippy::wrong_self_convention)]
    pub(crate) fn to_lowercase(
        this: &JsValue,
        _: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        // 3. Let sText be ! StringToCodePoints(S).
        // 4. Let lowerText be the result of toLowercase(sText), according to
        // the Unicode Default Case Conversion algorithm.
        // 5. Let L be ! CodePointsToString(lowerText).
        // 6. Return L.
        Ok(JsValue::new(string.to_lowercase()))
    }

    /// `String.prototype.toUpperCase()`
    ///
    /// The `toUpperCase()` method returns the calling string value converted to uppercase.
    ///
    /// The value will be **converted** to a string if it isn't one
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.toUppercase
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toUpperCase
    #[allow(clippy::wrong_self_convention)]
    pub(crate) fn to_uppercase(
        this: &JsValue,
        _: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // This function behaves in exactly the same way as `String.prototype.toLowerCase`, except that the String is
        // mapped using the toUppercase algorithm of the Unicode Default Case Conversion.

        // Comments below are an adaptation of the `String.prototype.toLowerCase` documentation.

        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        // 3. Let sText be ! StringToCodePoints(S).
        // 4. Let upperText be the result of toUppercase(sText), according to
        // the Unicode Default Case Conversion algorithm.
        // 5. Let L be ! CodePointsToString(upperText).
        // 6. Return L.
        Ok(JsValue::new(string.to_uppercase()))
    }

    /// `String.prototype.substring( indexStart[, indexEnd] )`
    ///
    /// The `substring()` method returns the part of the `string` between the start and end indexes, or to the end of the string.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.substring
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substring
    pub(crate) fn substring(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        // 3. Let len be the length of S.
        let len = string.encode_utf16().count() as i64;

        // 4. Let intStart be ? ToIntegerOrInfinity(start).
        let int_start = args.get_or_undefined(0).to_integer_or_infinity(context)?;

        // 5. If end is undefined, let intEnd be len; else let intEnd be ? ToIntegerOrInfinity(end).
        let int_end = match args.get_or_undefined(1) {
            &JsValue::Undefined => IntegerOrInfinity::Integer(len),
            end => end.to_integer_or_infinity(context)?,
        };

        // 6. Let finalStart be the result of clamping intStart between 0 and len.
        let final_start = int_start.clamp_finite(0, len) as usize;

        // 7. Let finalEnd be the result of clamping intEnd between 0 and len.
        let final_end = int_end.clamp_finite(0, len) as usize;

        // 8. Let from be min(finalStart, finalEnd).
        let from = min(final_start, final_end);

        // 9. Let to be max(finalStart, finalEnd).
        let to = max(final_start, final_end);

        // 10. Return the substring of S from from to to.
        // Extract the part of the string contained between the from index and the to index
        // where from is guaranteed to be smaller or equal to to
        // TODO: Full UTF-16 support
        let substring_utf16: Vec<u16> = string.encode_utf16().skip(from).take(to - from).collect();
        let substring = StdString::from_utf16_lossy(&substring_utf16);

        Ok(substring.into())
    }

    /// `String.prototype.substr( start[, length] )`
    ///
    /// The `substr()` method returns a portion of the string, starting at the specified index and extending for a given number of characters afterward.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.substr
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substr
    /// <https://tc39.es/ecma262/#sec-string.prototype.substr>
    pub(crate) fn substr(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let string = this.to_string(context)?;

        // 3. Let size be the length of S.
        let size = string.encode_utf16().count() as i64;

        // 4. Let intStart be ? ToIntegerOrInfinity(start).
        let int_start = args.get_or_undefined(0).to_integer_or_infinity(context)?;

        // 7. If length is undefined, let intLength be size; otherwise let intLength be ? ToIntegerOrInfinity(length).
        // Moved it before to ensure an error throws before returning the empty string on `match int_start`
        let int_length = match args.get_or_undefined(1) {
            &JsValue::Undefined => IntegerOrInfinity::Integer(size),
            val => val.to_integer_or_infinity(context)?,
        };

        let int_start = match int_start {
            // 6. Else if intStart < 0, set intStart to max(size + intStart, 0).
            IntegerOrInfinity::Integer(i) if i < 0 => max(size + i, 0),
            IntegerOrInfinity::Integer(i) => i,
            // 8. If intStart is +∞, ... return the empty String
            IntegerOrInfinity::PositiveInfinity => return Ok("".into()),
            // 5. If intStart is -∞, set intStart to 0.
            IntegerOrInfinity::NegativeInfinity => 0,
        } as usize;

        // 8. If ... intLength ≤ 0, or intLength is +∞, return the empty String.
        let int_length = match int_length {
            IntegerOrInfinity::Integer(i) if i > 0 => i,
            _ => return Ok("".into()),
        } as usize;

        // 9. Let intEnd be min(intStart + intLength, size).
        let int_end = min(int_start + int_length, size as usize);

        // 11. Return the substring of S from intStart to intEnd.
        // 10. If intStart ≥ intEnd, return the empty String.
        let substring_utf16: Vec<u16> = string
            .encode_utf16()
            .skip(int_start)
            .take(int_end - int_start)
            .collect();
        let substring = StdString::from_utf16_lossy(&substring_utf16);

        Ok(substring.into())
    }

    /// `String.prototype.split ( separator, limit )`
    ///
    /// The split() method divides a String into an ordered list of substrings, puts these substrings into an array, and returns the array.
    /// The division is done by searching for a pattern; where the pattern is provided as the first parameter in the method's call.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.split
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split
    pub(crate) fn split(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        let separator = args.get_or_undefined(0);
        let limit = args.get_or_undefined(1);

        // 2. If separator is neither undefined nor null, then
        if !separator.is_null_or_undefined() {
            // a. Let splitter be ? GetMethod(separator, @@split).
            let splitter = separator.get_method(WellKnownSymbols::split(), context)?;
            // b. If splitter is not undefined, then
            if let Some(splitter) = splitter {
                // i. Return ? Call(splitter, separator, « O, limit »).
                return splitter.call(separator, &[this.clone(), limit.clone()], context);
            }
        }

        // 3. Let S be ? ToString(O).
        let this_str = this.to_string(context)?;

        // 4. Let A be ! ArrayCreate(0).
        let a = Array::array_create(0, None, context)?;

        // 5. Let lengthA be 0.
        let mut length_a = 0;

        // 6.  If limit is undefined, let lim be 2^32 - 1; else let lim be ℝ(? ToUint32(limit)).
        let lim = if limit.is_undefined() {
            u32::MAX
        } else {
            limit.to_u32(context)?
        };

        // 7. Let R be ? ToString(separator).
        let separator_str = separator.to_string(context)?;

        // 8. If lim = 0, return A.
        if lim == 0 {
            return Ok(a.into());
        }

        // 9. If separator is undefined, then
        if separator.is_undefined() {
            // a. Perform ! CreateDataPropertyOrThrow(A, "0", S).
            a.create_data_property_or_throw(0, this_str, context)
                .expect("this CreateDataPropertyOrThrow call must not fail");

            // b. Return A.
            return Ok(a.into());
        }

        // 10. Let s be the length of S.
        let this_str_length = this_str.encode_utf16().count();

        // 11. If s = 0, then
        if this_str_length == 0 {
            // a. If R is not the empty String, then
            if !separator_str.is_empty() {
                // i. Perform ! CreateDataPropertyOrThrow(A, "0", S).
                a.create_data_property_or_throw(0, this_str, context)
                    .expect("this CreateDataPropertyOrThrow call must not fail");
            }

            // b. Return A.
            return Ok(a.into());
        }

        // 12. Let p be 0.
        // 13. Let q be p.
        let mut p = 0;
        let mut q = p;

        // 14. Repeat, while q ≠ s,
        while q != this_str_length {
            // a. Let e be SplitMatch(S, q, R).
            let e = split_match(&this_str, q, &separator_str);

            match e {
                // b. If e is not-matched, set q to q + 1.
                None => q += 1,
                // c. Else,
                Some(e) => {
                    // i. Assert: e is a non-negative integer ≤ s.
                    // ii. If e = p, set q to q + 1.
                    // iii. Else,
                    if e == p {
                        q += 1;
                    } else {
                        // 1. Let T be the substring of S from p to q.
                        let this_str_substring = StdString::from_utf16_lossy(
                            &this_str
                                .encode_utf16()
                                .skip(p)
                                .take(q - p)
                                .collect::<Vec<u16>>(),
                        );

                        // 2. Perform ! CreateDataPropertyOrThrow(A, ! ToString(𝔽(lengthA)), T).
                        a.create_data_property_or_throw(length_a, this_str_substring, context)
                            .expect("this CreateDataPropertyOrThrow call must not fail");

                        // 3. Set lengthA to lengthA + 1.
                        length_a += 1;

                        // 4. If lengthA = lim, return A.
                        if length_a == lim {
                            return Ok(a.into());
                        }

                        // 5. Set p to e.
                        p = e;

                        // 6. Set q to p.
                        q = p;
                    }
                }
            }
        }

        // 15. Let T be the substring of S from p to s.
        let this_str_substring = StdString::from_utf16_lossy(
            &this_str
                .encode_utf16()
                .skip(p)
                .take(this_str_length - p)
                .collect::<Vec<u16>>(),
        );

        // 16. Perform ! CreateDataPropertyOrThrow(A, ! ToString(𝔽(lengthA)), T).
        a.create_data_property_or_throw(length_a, this_str_substring, context)
            .expect("this CreateDataPropertyOrThrow call must not fail");

        // 17. Return A.
        Ok(a.into())
    }

    /// String.prototype.valueOf()
    ///
    /// The `valueOf()` method returns the primitive value of a `String` object.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.value_of
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/valueOf
    pub(crate) fn value_of(
        this: &JsValue,
        _: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Return ? thisStringValue(this value).
        Self::this_string_value(this, context).map(JsValue::from)
    }

    /// `String.prototype.matchAll( regexp )`
    ///
    /// The `matchAll()` method returns an iterator of all results matching a string against a [`regular expression`][regex], including [capturing groups][cg].
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.matchall
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/matchAll
    /// [regex]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions
    /// [cg]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions/Groups_and_Ranges
    pub(crate) fn match_all(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let o = this.require_object_coercible(context)?;

        // 2. If regexp is neither undefined nor null, then
        let regexp = args.get_or_undefined(0);
        if !regexp.is_null_or_undefined() {
            // a. Let isRegExp be ? IsRegExp(regexp).
            // b. If isRegExp is true, then
            if let Some(regexp_obj) = regexp.as_object().filter(|obj| obj.is_regexp()) {
                // i. Let flags be ? Get(regexp, "flags").
                let flags = regexp_obj.get("flags", context)?;

                // ii. Perform ? RequireObjectCoercible(flags).
                flags.require_object_coercible(context)?;

                // iii. If ? ToString(flags) does not contain "g", throw a TypeError exception.
                if !flags.to_string(context)?.contains('g') {
                    return context.throw_type_error(
                        "String.prototype.matchAll called with a non-global RegExp argument",
                    );
                }
            }
            // c. Let matcher be ? GetMethod(regexp, @@matchAll).
            let matcher = regexp.get_method(WellKnownSymbols::match_all(), context)?;
            // d. If matcher is not undefined, then
            if let Some(matcher) = matcher {
                return matcher.call(regexp, &[o.clone()], context);
            }
        }

        // 3. Let S be ? ToString(O).
        let s = o.to_string(context)?;

        // 4. Let rx be ? RegExpCreate(regexp, "g").
        let rx = RegExp::create(regexp, &JsValue::new("g"), context)?;

        // 5. Return ? Invoke(rx, @@matchAll, « S »).
        rx.invoke(WellKnownSymbols::match_all(), &[JsValue::new(s)], context)
    }

    /// `String.prototype.normalize( [ form ] )`
    ///
    /// The normalize() method normalizes a string into a form specified in the Unicode® Standard Annex #15
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.normalize
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/normalize
    pub(crate) fn normalize(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let this = this.require_object_coercible(context)?;

        // 2. Let S be ? ToString(O).
        let s = this.to_string(context)?;

        let form = args.get_or_undefined(0);

        let f_str;

        let f = if form.is_undefined() {
            // 3. If form is undefined, let f be "NFC".
            "NFC"
        } else {
            // 4. Else, let f be ? ToString(form).
            f_str = form.to_string(context)?;
            f_str.as_str()
        };

        // 6. Let ns be the String value that is the result of normalizing S
        // into the normalization form named by f as specified in
        // https://unicode.org/reports/tr15/.
        // 7. Return ns.
        match f {
            "NFC" => Ok(JsValue::new(s.nfc().collect::<StdString>())),
            "NFD" => Ok(JsValue::new(s.nfd().collect::<StdString>())),
            "NFKC" => Ok(JsValue::new(s.nfkc().collect::<StdString>())),
            "NFKD" => Ok(JsValue::new(s.nfkd().collect::<StdString>())),
            // 5. If f is not one of "NFC", "NFD", "NFKC", or "NFKD", throw a RangeError exception.
            _ => context
                .throw_range_error("The normalization form should be one of NFC, NFD, NFKC, NFKD."),
        }
    }

    /// `String.prototype.search( regexp )`
    ///
    /// The search() method executes a search for a match between a regular expression and this String object.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-string.prototype.search
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/search
    pub(crate) fn search(
        this: &JsValue,
        args: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        // 1. Let O be ? RequireObjectCoercible(this value).
        let o = this.require_object_coercible(context)?;

        // 2. If regexp is neither undefined nor null, then
        let regexp = args.get_or_undefined(0);
        if !regexp.is_null_or_undefined() {
            // a. Let searcher be ? GetMethod(regexp, @@search).
            let searcher = regexp.get_method(WellKnownSymbols::search(), context)?;
            // b. If searcher is not undefined, then
            if let Some(searcher) = searcher {
                // i. Return ? Call(searcher, regexp, « O »).
                return searcher.call(regexp, &[o.clone()], context);
            }
        }

        // 3. Let string be ? ToString(O).
        let string = o.to_string(context)?;

        // 4. Let rx be ? RegExpCreate(regexp, undefined).
        let rx = RegExp::create(regexp, &JsValue::Undefined, context)?;

        // 5. Return ? Invoke(rx, @@search, « string »).
        rx.invoke(WellKnownSymbols::search(), &[JsValue::new(string)], context)
    }

    pub(crate) fn iterator(
        this: &JsValue,
        _: &[JsValue],
        context: &mut Context,
    ) -> JsResult<JsValue> {
        StringIterator::create_string_iterator(this.clone(), context)
    }
}

/// Abstract operation `GetSubstitution ( matched, str, position, captures, namedCaptures, replacement )`
///
/// More information:
///  - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-getsubstitution
pub(crate) fn get_substitution(
    matched: &str,
    str: &str,
    position: usize,
    captures: &[JsValue],
    named_captures: &JsValue,
    replacement: &JsString,
    context: &mut Context,
) -> JsResult<JsString> {
    // 1. Assert: Type(matched) is String.

    // 2. Let matchLength be the number of code units in matched.
    let match_length = matched.encode_utf16().count();

    // 3. Assert: Type(str) is String.

    // 4. Let stringLength be the number of code units in str.
    let str_length = str.encode_utf16().count();

    // 5. Assert: position ≤ stringLength.
    // 6. Assert: captures is a possibly empty List of Strings.
    // 7. Assert: Type(replacement) is String.

    // 8. Let tailPos be position + matchLength.
    let tail_pos = position + match_length;

    // 9. Let m be the number of elements in captures.
    let m = captures.len();

    // 10. Let result be the String value derived from replacement by copying code unit elements
    //     from replacement to result while performing replacements as specified in Table 58.
    //     These $ replacements are done left-to-right, and, once such a replacement is performed,
    //     the new replacement text is not subject to further replacements.
    let mut result = StdString::new();
    let mut chars = replacement.chars().peekable();

    while let Some(first) = chars.next() {
        if first == '$' {
            let second = chars.next();
            let second_is_digit = second.as_ref().map_or(false, char::is_ascii_digit);
            // we use peek so that it is still in the iterator if not used
            let third = if second_is_digit { chars.peek() } else { None };
            let third_is_digit = third.map_or(false, char::is_ascii_digit);

            match (second, third) {
                // $$
                (Some('$'), _) => {
                    // $
                    result.push('$');
                }
                // $&
                (Some('&'), _) => {
                    // matched
                    result.push_str(matched);
                }
                // $`
                (Some('`'), _) => {
                    // The replacement is the substring of str from 0 to position.
                    result.push_str(&StdString::from_utf16_lossy(
                        &str.encode_utf16().take(position).collect::<Vec<u16>>(),
                    ));
                }
                // $'
                (Some('\''), _) => {
                    // If tailPos ≥ stringLength, the replacement is the empty String.
                    // Otherwise the replacement is the substring of str from tailPos.
                    if tail_pos < str_length {
                        result.push_str(&StdString::from_utf16_lossy(
                            &str.encode_utf16().skip(tail_pos).collect::<Vec<u16>>(),
                        ));
                    }
                }
                // $nn
                (Some(second), Some(third)) if second_is_digit && third_is_digit => {
                    // The nnth element of captures, where nn is a two-digit decimal number in the range 01 to 99.
                    let tens = second
                        .to_digit(10)
                        .expect("could not convert character to digit after checking it")
                        as usize;
                    let units = third
                        .to_digit(10)
                        .expect("could not convert character to digit after checking it")
                        as usize;
                    let nn = 10 * tens + units;

                    // If nn ≤ m and the nnth element of captures is undefined, use the empty String instead.
                    // If nn is 00 or nn > m, no replacement is done.
                    if nn == 0 || nn > m {
                        result.push('$');
                        result.push(second);
                        result.push(*third);
                    } else if let Some(capture) = captures.get(nn - 1) {
                        if let Some(s) = capture.as_string() {
                            result.push_str(s);
                        }
                    }

                    chars.next();
                }
                // $n
                (Some(second), _) if second_is_digit => {
                    // The nth element of captures, where n is a single digit in the range 1 to 9.
                    let n = second
                        .to_digit(10)
                        .expect("could not convert character to digit after checking it")
                        as usize;

                    // If n ≤ m and the nth element of captures is undefined, use the empty String instead.
                    // If n > m, no replacement is done.
                    if n == 0 || n > m {
                        result.push('$');
                        result.push(second);
                    } else if let Some(capture) = captures.get(n - 1) {
                        if let Some(s) = capture.as_string() {
                            result.push_str(s);
                        }
                    }
                }
                // $<
                (Some('<'), _) => {
                    // 1. If namedCaptures is undefined, the replacement text is the String "$<".
                    // 2. Else,
                    if named_captures.is_undefined() {
                        result.push_str("$<");
                    } else {
                        // a. Assert: Type(namedCaptures) is Object.
                        let named_captures = named_captures
                            .as_object()
                            .expect("should be an object according to spec");

                        // b. Scan until the next > U+003E (GREATER-THAN SIGN).
                        let mut group_name = StdString::new();
                        let mut found = false;
                        loop {
                            match chars.next() {
                                Some('>') => {
                                    found = true;
                                    break;
                                }
                                Some(c) => group_name.push(c),
                                None => break,
                            }
                        }

                        // c. If none is found, the replacement text is the String "$<".
                        #[allow(clippy::if_not_else)]
                        if !found {
                            result.push_str("$<");
                            result.push_str(&group_name);
                        // d. Else,
                        } else {
                            // i. Let groupName be the enclosed substring.
                            // ii. Let capture be ? Get(namedCaptures, groupName).
                            let capture = named_captures.get(group_name, context)?;

                            // iii. If capture is undefined, replace the text through > with the empty String.
                            // iv. Otherwise, replace the text through > with ? ToString(capture).
                            if !capture.is_undefined() {
                                result.push_str(capture.to_string(context)?.as_str());
                            }
                        }
                    }
                }
                // $?, ? is none of the above
                _ => {
                    result.push('$');
                    if let Some(second) = second {
                        result.push(second);
                    }
                }
            }
        } else {
            result.push(first);
        }
    }

    // 11. Return result.
    Ok(result.into())
}

/// `22.1.3.21.1 SplitMatch ( S, q, R )`
///
/// More information:
///  - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-splitmatch
fn split_match(s_str: &str, q: usize, r_str: &str) -> Option<usize> {
    // 1. Let r be the number of code units in R.
    let r = r_str.encode_utf16().count();

    // 2. Let s be the number of code units in S.
    let s = s_str.encode_utf16().count();

    // 3. If q + r > s, return not-matched.
    if q + r > s {
        return None;
    }

    // 4. If there exists an integer i between 0 (inclusive) and r (exclusive)
    //    such that the code unit at index q + i within S is different from the code unit at index i within R,
    //    return not-matched.
    for i in 0..r {
        if let Some(s_char) = s_str.encode_utf16().nth(q + i) {
            if let Some(r_char) = r_str.encode_utf16().nth(i) {
                if s_char != r_char {
                    return None;
                }
            }
        }
    }

    // 5. Return q + r.
    Some(q + r)
}

/// Abstract operation `IsRegExp( argument )`
///
/// More information:
/// [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-isregexp
fn is_reg_exp(argument: &JsValue, context: &mut Context) -> JsResult<bool> {
    // 1. If Type(argument) is not Object, return false.
    let argument = match argument {
        JsValue::Object(o) => o,
        _ => return Ok(false),
    };

    is_reg_exp_object(argument, context)
}
fn is_reg_exp_object(argument: &JsObject, context: &mut Context) -> JsResult<bool> {
    // 2. Let matcher be ? Get(argument, @@match).
    let matcher = argument.get(WellKnownSymbols::r#match(), context)?;

    // 3. If matcher is not undefined, return ! ToBoolean(matcher).
    if !matcher.is_undefined() {
        return Ok(matcher.to_boolean());
    }

    // 4. If argument has a [[RegExpMatcher]] internal slot, return true.
    // 5. Return false.
    Ok(argument.is_regexp())
}