Struct wasm_bindgen::JsValue

pub struct JsValue { /* private fields */ }

Representation of an object owned by JS.

A JsValue doesn’t actually live in Rust right now but actually in a table owned by the wasm-bindgen generated JS glue code. Eventually the ownership will transfer into wasm directly and this will likely become more efficient, but for now it may be slightly slow.

Implementations

impl JsValue

pub const NULL: JsValue = _

The null JS value constant.

pub const UNDEFINED: JsValue = _

The undefined JS value constant.

pub const TRUE: JsValue = _

The true JS value constant.

pub const FALSE: JsValue = _

The false JS value constant.

pub fn from_str(s: &str) -> JsValue

Creates a new JS value which is a string.

The utf-8 string provided is copied to the JS heap and the string will be owned by the JS garbage collector.

pub fn from_f64(n: f64) -> JsValue

Creates a new JS value which is a number.

This function creates a JS value representing a number (a heap allocated number) and returns a handle to the JS version of it.

pub fn from_bool(b: bool) -> JsValue

Creates a new JS value which is a boolean.

This function creates a JS object representing a boolean (a heap allocated boolean) and returns a handle to the JS version of it.

pub fn undefined() -> JsValue

Creates a new JS value representing undefined.

pub fn null() -> JsValue

Creates a new JS value representing null.

pub fn symbol(description: Option<&str>) -> JsValue

Creates a new JS symbol with the optional description specified.

This function will invoke the Symbol constructor in JS and return the JS object corresponding to the symbol created.

pub fn from_serde<T>(t: &T) -> Result<JsValue>where
    T: Serialize + ?Sized,

Creates a new JsValue from the JSON serialization of the object t provided.

This function will serialize the provided value t to a JSON string, send the JSON string to JS, parse it into a JS object, and then return a handle to the JS object. This is unlikely to be super speedy so it’s not recommended for large payloads, but it’s a nice to have in some situations!

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

Errors

Returns any error encountered when serializing T into JSON.

pub fn into_serde<T>(&self) -> Result<T>where
    T: for<'a> Deserialize<'a>,

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

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 as_js_string() method instead.

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

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_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_function(&self) -> bool

Tests whether the type of this JS value is function.

Trait Implementations

impl<T: ?Sized> AsRef<JsValue> for Closure<T>

fn as_ref(&self) -> &JsValue

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

impl AsRef<JsValue> for JsValue

fn as_ref(&self) -> &JsValue

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

impl Clone for JsValue

fn clone(&self) -> JsValue

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for JsValue

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

Formats the value using the given formatter.

impl Drop for JsValue

fn drop(&mut self)

Executes the destructor for this type.

impl<'a> From<&'a String> for JsValue

fn from(s: &'a String) -> JsValue

Converts to this type from the input type.

impl<'a, T> From<&'a T> for JsValuewhere
    T: JsCast,

fn from(s: &'a T) -> JsValue

Converts to this type from the input type.

impl<'a> From<&'a str> for JsValue

fn from(s: &'a str) -> JsValue

Converts to this type from the input type.

impl<T> From<Option<T>> for JsValuewhere
    JsValue: From<T>,

fn from(s: Option<T>) -> JsValue

Converts to this type from the input type.

impl From<String> for JsValue

fn from(s: String) -> JsValue

Converts to this type from the input type.

impl From<bool> for JsValue

fn from(s: bool) -> JsValue

Converts to this type from the input type.

impl From<f32> for JsValue

fn from(n: f32) -> JsValue

Converts to this type from the input type.

impl From<f64> for JsValue

fn from(n: f64) -> JsValue

Converts to this type from the input type.

impl From<i16> for JsValue

fn from(n: i16) -> JsValue

Converts to this type from the input type.

impl From<i32> for JsValue

fn from(n: i32) -> JsValue

Converts to this type from the input type.

impl From<i8> for JsValue

fn from(n: i8) -> JsValue

Converts to this type from the input type.

impl From<u16> for JsValue

fn from(n: u16) -> JsValue

Converts to this type from the input type.

impl From<u32> for JsValue

fn from(n: u32) -> JsValue

Converts to this type from the input type.

impl From<u8> for JsValue

fn from(n: u8) -> JsValue

Converts to this type from the input type.

impl FromWasmAbi for JsValue

type Abi = u32

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

unsafe fn from_abi(js: u32, _extra: &mut dyn Stack) -> JsValue

Recover a Self from Self::Abi.

impl<'a> IntoWasmAbi for &'a JsValue

type Abi = u32

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

fn into_abi(self, _extra: &mut dyn Stack) -> u32

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

impl IntoWasmAbi for JsValue

type Abi = u32

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

fn into_abi(self, _extra: &mut dyn Stack) -> u32

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

impl JsCast for JsValue

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 is_instance_of<T>(&self) -> boolwhere
    T: JsCast,

Test whether this JS value is an instance of the 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) -> Twhere
    T: JsCast,

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

fn unchecked_ref<T>(&self) -> &Twhere
    T: JsCast,

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

impl<'a> PartialEq<&'a String> for JsValue

fn eq(&self, other: &&'a String) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl<'a> PartialEq<&'a str> for JsValue

fn eq(&self, other: &&'a str) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<JsValue> for JsValue

fn eq(&self, other: &JsValue) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<String> for JsValue

fn eq(&self, other: &String) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<bool> for JsValue

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

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<f32> for JsValue

fn eq(&self, other: &f32) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<f64> for JsValue

fn eq(&self, other: &f64) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<i16> for JsValue

fn eq(&self, other: &i16) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<i32> for JsValue

fn eq(&self, other: &i32) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<i8> for JsValue

fn eq(&self, other: &i8) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<str> for JsValue

fn eq(&self, other: &str) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<u16> for JsValue

fn eq(&self, other: &u16) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<u32> for JsValue

fn eq(&self, other: &u32) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialEq<u8> for JsValue

fn eq(&self, other: &u8) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

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

impl RefFromWasmAbi for JsValue

type Abi = u32

The wasm ABI type references to Self are recovered from.

type Anchor = ManuallyDrop<JsValue>

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: u32, _extra: &mut dyn Stack) -> Self::Anchor

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