Struct JsOption 

pub struct JsOption<T = JsValue> { /* private fields */ }

A nullable JS value of type T.

Unlike Option<T>, which is a Rust-side construct, JsOption<T> represents a JS value that may be T, null, or undefined, where the null status is not yet known in Rust. The value remains in JS until inspected via methods like is_empty, as_option, or into_option.

T must implement JsGeneric, meaning it is any type that can be represented as a JsValue (e.g., JsString, Number, Object, etc.). JsOption<T> itself implements JsGeneric, so it can be used in all generic positions that accept JS types.

Implementations

impl<T> JsOption<T>

pub fn new() -> Self

Creates an empty JsOption<T> representing null.

pub fn wrap(val: T) -> Self

Wraps a value in a JsOption<T>.

pub fn from_option(opt: Option<T>) -> Self

Creates a JsOption<T> from an Option<T>.

Returns JsOption::wrap(val) if Some(val), otherwise JsOption::new().

pub fn is_empty(&self) -> bool

Tests whether this JsOption<T> is empty (null or undefined).

pub fn as_option(&self) -> Option<T>

Converts this JsOption<T> to an Option<T> by cloning the inner value.

Returns None if the value is null or undefined, otherwise returns Some(T) with a clone of the contained value.

pub fn into_option(self) -> Option<T>

Converts this JsOption<T> into an Option<T>, consuming self.

Returns None if the value is null or undefined, otherwise returns Some(T) with the contained value.

pub fn unwrap(self) -> T

Returns the contained value, consuming self.

Panics

Panics if the value is null or undefined.

pub fn expect(self, msg: &str) -> T

Returns the contained value, consuming self.

Panics

Panics if the value is null or undefined, with a panic message including the passed message.

pub fn unwrap_or_default(self) -> T

where T: Default,

Returns the contained value or a default.

Returns the contained value if not null or undefined, otherwise returns the default value of T.

pub fn unwrap_or_else<F>(self, f: F) -> T

where F: FnOnce() -> T,

Returns the contained value or computes it from a closure.

Returns the contained value if not null or undefined, otherwise calls f and returns the result.

Methods from Deref<Target = JsValue>

pub const NULL: JsValue

pub const UNDEFINED: JsValue

pub const TRUE: JsValue

pub const FALSE: JsValue

pub fn into_serde<T>(&self) -> Result<T>

where T: for<'a> Deserialize<'a>,

👎Deprecated: causes dependency cycles, use serde-wasm-bindgen or gloo_utils::format::JsValueSerdeExt instead

Invokes JSON.stringify on this value and then parses the resulting JSON into an arbitrary Rust value.

This function is deprecated, due to creating a dependency cycle in some circumstances. Use serde-wasm-bindgen or gloo_utils::format::JsValueSerdeExt instead.

This function will first call JSON.stringify on the JsValue itself. The resulting string is then passed into Rust which then parses it as JSON into the resulting value.

Usage of this API requires activating the serde-serialize feature of the wasm-bindgen crate.

Errors

Returns any error encountered when parsing the JSON into a T.

pub fn as_f64(&self) -> Option<f64>

Returns the f64 value of this JS value if it’s an instance of a number.

If this JS value is not an instance of a number then this returns None.

pub fn is_string(&self) -> bool

Tests whether this JS value is a JS string.

pub fn as_string(&self) -> Option<String>

If this JS value is a string value, this function copies the JS string value into Wasm linear memory, encoded as UTF-8, and returns it as a Rust String.

To avoid the copying and re-encoding, consider the JsString::try_from() function from js-sys instead.

If this JS value is not an instance of a string or if it’s not valid utf-8 then this returns None.

UTF-16 vs UTF-8

JavaScript strings in general are encoded as UTF-16, but Rust strings are encoded as UTF-8. This can cause the Rust string to look a bit different than the JS string sometimes. For more details see the documentation about the str type which contains a few caveats about the encodings.

pub fn as_bool(&self) -> Option<bool>

Returns the bool value of this JS value if it’s an instance of a boolean.

If this JS value is not an instance of a boolean then this returns None.

pub fn is_null(&self) -> bool

Tests whether this JS value is null

pub fn is_undefined(&self) -> bool

Tests whether this JS value is undefined

pub fn is_null_or_undefined(&self) -> bool

Tests whether this JS value is null or undefined

pub fn is_symbol(&self) -> bool

Tests whether the type of this JS value is symbol

pub fn is_object(&self) -> bool

Tests whether typeof self == "object" && self !== null.

pub fn is_array(&self) -> bool

Tests whether this JS value is an instance of Array.

pub fn is_function(&self) -> bool

Tests whether the type of this JS value is function.

pub fn is_bigint(&self) -> bool

Tests whether the type of this JS value is bigint.

pub fn js_typeof(&self) -> JsValue

Applies the unary typeof JS operator on a JsValue.

MDN documentation

pub fn js_in(&self, obj: &JsValue) -> bool

Applies the binary in JS operator on the two JsValues.

MDN documentation

pub fn is_truthy(&self) -> bool

Tests whether the value is “truthy”.

pub fn is_falsy(&self) -> bool

Tests whether the value is “falsy”.

pub fn loose_eq(&self, other: &Self) -> bool

Compare two JsValues for equality, using the == operator in JS.

MDN documentation

pub fn bit_not(&self) -> JsValue

Applies the unary ~ JS operator on a JsValue.

MDN documentation

pub fn unsigned_shr(&self, rhs: &Self) -> u32

Applies the binary >>> JS operator on the two JsValues.

MDN documentation

pub fn checked_div(&self, rhs: &Self) -> Self

Applies the binary / JS operator on two JsValues, catching and returning any RangeError thrown.

MDN documentation

pub fn pow(&self, rhs: &Self) -> Self

Applies the binary ** JS operator on the two JsValues.

MDN documentation

pub fn lt(&self, other: &Self) -> bool

Applies the binary < JS operator on the two JsValues.

MDN documentation

pub fn le(&self, other: &Self) -> bool

Applies the binary <= JS operator on the two JsValues.

MDN documentation

pub fn ge(&self, other: &Self) -> bool

Applies the binary >= JS operator on the two JsValues.

MDN documentation

pub fn gt(&self, other: &Self) -> bool

Applies the binary > JS operator on the two JsValues.

MDN documentation

pub fn unchecked_into_f64(&self) -> f64

Applies the unary + JS operator on a JsValue. Can throw.

MDN documentation

Trait Implementations

impl<T> AsRef<JsOption<T>> for JsOption<T>

fn as_ref(&self) -> &JsOption<T>

Converts this type into a shared reference of the (usually inferred) input type.

impl<T> AsRef<JsValue> for JsOption<T>

fn as_ref(&self) -> &JsValue

Converts this type into a shared reference of the (usually inferred) input type.

impl<T: Clone> Clone for JsOption<T>

fn clone(&self) -> JsOption<T>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: JsGeneric + Debug> Debug for JsOption<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: JsGeneric> Default for JsOption<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T> Deref for JsOption<T>

type Target = JsValue

The resulting type after dereferencing.

fn deref(&self) -> &JsValue

Dereferences the value.

impl<T: JsGeneric + Display> Display for JsOption<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> ErasableGeneric for JsOption<T>

type Repr = JsValue

The singular concrete type that all generic variants can be transmuted on

impl<T> From<JsOption<T>> for JsValue

fn from(obj: JsOption<T>) -> JsValue

Converts to this type from the input type.

impl From<JsValue> for JsOption

fn from(obj: JsValue) -> Self

Converts to this type from the input type.

impl<T> FromWasmAbi for JsOption<T>

type Abi = <JsValue as FromWasmAbi>::Abi

The Wasm ABI type that this converts from when coming back out from the ABI boundary.

unsafe fn from_abi(js: Self::Abi) -> Self

Recover a Self from Self::Abi.

impl<'a, T> IntoWasmAbi for &'a JsOption<T>

type Abi = <&'a JsValue as IntoWasmAbi>::Abi

The Wasm ABI type that this converts into when crossing the ABI boundary.

fn into_abi(self) -> Self::Abi

Convert self into Self::Abi so that it can be sent across the wasm ABI boundary.

impl<T> IntoWasmAbi for JsOption<T>

type Abi = <JsValue as IntoWasmAbi>::Abi

The Wasm ABI type that this converts into when crossing the ABI boundary.

fn into_abi(self) -> Self::Abi

Convert self into Self::Abi so that it can be sent across the wasm ABI boundary.

impl<T> JsCast for JsOption<T>

fn instanceof(val: &JsValue) -> bool

Performs a dynamic instanceof check to see whether the JsValue provided is an instance of this type.

fn unchecked_from_js(val: JsValue) -> Self

Performs a zero-cost unchecked conversion from a JsValue into an instance of Self

fn unchecked_from_js_ref(val: &JsValue) -> &Self

Performs a zero-cost unchecked conversion from a &JsValue into an instance of &Self.

fn has_type<T>(&self) -> bool

where T: JsCast,

Test whether this JS value has a type T.

fn dyn_into<T>(self) -> Result<T, Self>

where T: JsCast,

Performs a dynamic cast (checked at runtime) of this value into the target type T.

fn dyn_ref<T>(&self) -> Option<&T>

where T: JsCast,

Performs a dynamic cast (checked at runtime) of this value into the target type T.

fn unchecked_into<T>(self) -> T

where T: JsCast,

Performs a zero-cost unchecked cast into the specified type.

fn unchecked_ref<T>(&self) -> &T

where T: JsCast,

Performs a zero-cost unchecked cast into a reference to the specified type.

fn is_instance_of<T>(&self) -> bool

where T: JsCast,

Test whether this JS value is an instance of the type T.

fn is_type_of(val: &JsValue) -> bool

Performs a dynamic check to see whether the JsValue provided is a value of this type.

impl<T> LongRefFromWasmAbi for JsOption<T>

type Abi = <JsValue as LongRefFromWasmAbi>::Abi

Same as RefFromWasmAbi::Abi

type Anchor = JsOption<T>

Same as RefFromWasmAbi::Anchor

unsafe fn long_ref_from_abi(js: Self::Abi) -> Self::Anchor

Same as RefFromWasmAbi::ref_from_abi

impl<T> OptionFromWasmAbi for JsOption<T>

fn is_none(abi: &Self::Abi) -> bool

Tests whether the argument is a “none” instance. If so it will be deserialized as None, and otherwise it will be passed to FromWasmAbi.

impl<'a, T> OptionIntoWasmAbi for &'a JsOption<T>

fn none() -> Self::Abi

Returns an ABI instance indicating “none”, which JS will interpret as the None branch of this option.

impl<T> OptionIntoWasmAbi for JsOption<T>

fn none() -> Self::Abi

Returns an ABI instance indicating “none”, which JS will interpret as the None branch of this option.

impl<T: PartialEq> PartialEq for JsOption<T>

fn eq(&self, other: &JsOption<T>) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T> Promising for JsOption<T>

type Resolution = JsOption<T>

The type that this value resolves to.

impl<T> RefFromWasmAbi for JsOption<T>

type Abi = <JsValue as RefFromWasmAbi>::Abi

The Wasm ABI type references to Self are recovered from.

type Anchor = ManuallyDrop<JsOption<T>>

The type that holds the reference to Self for the duration of the invocation of the function that has an &Self parameter. This is required to ensure that the lifetimes don’t persist beyond one function call, and so that they remain anonymous.

unsafe fn ref_from_abi(js: Self::Abi) -> Self::Anchor

Recover a Self::Anchor from Self::Abi.

impl<T> StructuralPartialEq for JsOption<T>

impl<T> UpcastFrom<()> for JsOption<T>

impl<T1, Target1> UpcastFrom<(T1,)> for JsOption<(Target1,)>

where Target1: JsGeneric + UpcastFrom<T1>, T1: JsGeneric,

impl<T1, T2, Target1, Target2> UpcastFrom<(T1, T2)> for JsOption<(Target1, Target2)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, T1: JsGeneric, T2: JsGeneric,

impl<T1, T2, T3, Target1, Target2, Target3> UpcastFrom<(T1, T2, T3)> for JsOption<(Target1, Target2, Target3)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric,

impl<T1, T2, T3, T4, Target1, Target2, Target3, Target4> UpcastFrom<(T1, T2, T3, T4)> for JsOption<(Target1, Target2, Target3, Target4)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, Target4: JsGeneric + UpcastFrom<T4>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric, T4: JsGeneric,

impl<T1, T2, T3, T4, T5, Target1, Target2, Target3, Target4, Target5> UpcastFrom<(T1, T2, T3, T4, T5)> for JsOption<(Target1, Target2, Target3, Target4, Target5)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, Target4: JsGeneric + UpcastFrom<T4>, Target5: JsGeneric + UpcastFrom<T5>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric, T4: JsGeneric, T5: JsGeneric,

impl<T1, T2, T3, T4, T5, T6, Target1, Target2, Target3, Target4, Target5, Target6> UpcastFrom<(T1, T2, T3, T4, T5, T6)> for JsOption<(Target1, Target2, Target3, Target4, Target5, Target6)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, Target4: JsGeneric + UpcastFrom<T4>, Target5: JsGeneric + UpcastFrom<T5>, Target6: JsGeneric + UpcastFrom<T6>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric, T4: JsGeneric, T5: JsGeneric, T6: JsGeneric,

impl<T1, T2, T3, T4, T5, T6, T7, Target1, Target2, Target3, Target4, Target5, Target6, Target7> UpcastFrom<(T1, T2, T3, T4, T5, T6, T7)> for JsOption<(Target1, Target2, Target3, Target4, Target5, Target6, Target7)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, Target4: JsGeneric + UpcastFrom<T4>, Target5: JsGeneric + UpcastFrom<T5>, Target6: JsGeneric + UpcastFrom<T6>, Target7: JsGeneric + UpcastFrom<T7>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric, T4: JsGeneric, T5: JsGeneric, T6: JsGeneric, T7: JsGeneric,

impl<T1, T2, T3, T4, T5, T6, T7, T8, Target1, Target2, Target3, Target4, Target5, Target6, Target7, Target8> UpcastFrom<(T1, T2, T3, T4, T5, T6, T7, T8)> for JsOption<(Target1, Target2, Target3, Target4, Target5, Target6, Target7, Target8)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, Target4: JsGeneric + UpcastFrom<T4>, Target5: JsGeneric + UpcastFrom<T5>, Target6: JsGeneric + UpcastFrom<T6>, Target7: JsGeneric + UpcastFrom<T7>, Target8: JsGeneric + UpcastFrom<T8>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric, T4: JsGeneric, T5: JsGeneric, T6: JsGeneric, T7: JsGeneric, T8: JsGeneric,

impl<T, Target> UpcastFrom<*const T> for JsOption<*const Target>

where Target: UpcastFrom<T>,

impl UpcastFrom<JsError> for JsOption<JsValue>

impl<T> UpcastFrom<JsOption<T>> for JsValue

impl<T, U> UpcastFrom<JsOption<U>> for JsOption<T>

where T: UpcastFrom<U>,

impl UpcastFrom<JsValue> for JsOption<JsValue>

impl<T> UpcastFrom<Null> for JsOption<T>

impl<T, Target> UpcastFrom<Option<T>> for JsOption<Option<Target>>

where Target: UpcastFrom<T>,

impl<T, E, TargetT, TargetE> UpcastFrom<Result<T, E>> for JsOption<Result<TargetT, TargetE>>

where TargetT: UpcastFrom<T>, TargetE: UpcastFrom<E>,

impl<T> UpcastFrom<Undefined> for JsOption<T>

impl UpcastFrom<bool> for JsOption<JsValue>

impl UpcastFrom<char> for JsOption<JsValue>

impl UpcastFrom<f32> for JsOption<JsValue>

impl UpcastFrom<f32> for JsOption<f64>

impl UpcastFrom<f64> for JsOption<JsValue>

impl UpcastFrom<i128> for JsOption<JsValue>

impl UpcastFrom<i16> for JsOption<JsValue>

impl UpcastFrom<i16> for JsOption<i128>

impl UpcastFrom<i16> for JsOption<i32>

impl UpcastFrom<i16> for JsOption<i64>

impl UpcastFrom<i32> for JsOption<JsValue>

impl UpcastFrom<i32> for JsOption<i128>

impl UpcastFrom<i32> for JsOption<i64>

impl UpcastFrom<i32> for JsOption<isize>

impl UpcastFrom<i64> for JsOption<JsValue>

impl UpcastFrom<i64> for JsOption<i128>

impl UpcastFrom<i8> for JsOption<JsValue>

impl UpcastFrom<i8> for JsOption<i128>

impl UpcastFrom<i8> for JsOption<i16>

impl UpcastFrom<i8> for JsOption<i32>

impl UpcastFrom<i8> for JsOption<i64>

impl UpcastFrom<isize> for JsOption<JsValue>

impl UpcastFrom<isize> for JsOption<i128>

impl UpcastFrom<isize> for JsOption<i64>

impl UpcastFrom<u128> for JsOption<JsValue>

impl UpcastFrom<u16> for JsOption<JsValue>

impl UpcastFrom<u16> for JsOption<u128>

impl UpcastFrom<u16> for JsOption<u32>

impl UpcastFrom<u16> for JsOption<u64>

impl UpcastFrom<u32> for JsOption<JsValue>

impl UpcastFrom<u32> for JsOption<u128>

impl UpcastFrom<u32> for JsOption<u64>

impl UpcastFrom<u32> for JsOption<usize>

impl UpcastFrom<u64> for JsOption<JsValue>

impl UpcastFrom<u64> for JsOption<u128>

impl UpcastFrom<u8> for JsOption<JsValue>

impl UpcastFrom<u8> for JsOption<u128>

impl UpcastFrom<u8> for JsOption<u16>

impl UpcastFrom<u8> for JsOption<u32>

impl UpcastFrom<u8> for JsOption<u64>

impl UpcastFrom<usize> for JsOption<JsValue>

impl UpcastFrom<usize> for JsOption<u128>

impl UpcastFrom<usize> for JsOption<u64>