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 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_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.

pub fn is_truthy(&self) -> bool

Tests whether the value is “truthy”.

pub fn is_falsy(&self) -> bool

Tests whether the value is “falsy”.

Trait Implementations

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

fn as_ref(&self) -> &JsValue

Performs the conversion.

impl AsRef<JsValue> for JsValue

fn as_ref(&self) -> &JsValue

Performs the conversion.

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 Default for JsValue

fn default() -> Self

Returns the “default value” for a type.

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

Performs the conversion.

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

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

Performs the conversion.

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

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

Performs the conversion.

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

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

Performs the conversion.

impl From<String> for JsValue

fn from(s: String) -> JsValue

Performs the conversion.

impl From<bool> for JsValue

fn from(s: bool) -> JsValue

Performs the conversion.

impl From<f32> for JsValue

fn from(n: f32) -> JsValue

Performs the conversion.

impl From<f64> for JsValue

fn from(n: f64) -> JsValue

Performs the conversion.

impl From<i16> for JsValue

fn from(n: i16) -> JsValue

Performs the conversion.

impl From<i32> for JsValue

fn from(n: i32) -> JsValue

Performs the conversion.

impl From<i8> for JsValue

fn from(n: i8) -> JsValue

Performs the conversion.

impl From<u16> for JsValue

fn from(n: u16) -> JsValue

Performs the conversion.

impl From<u32> for JsValue

fn from(n: u32) -> JsValue

Performs the conversion.

impl From<u8> for JsValue

fn from(n: u8) -> JsValue

Performs the conversion.

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) -> JsValue

Recover a Self from Self::Abi.

impl IntoWasmAbi for JsValue

type Abi = u32

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

fn into_abi(self) -> u32

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

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) -> 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 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<'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 !=.

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 !=.

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 !=.

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 !=.

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 !=.

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 !=.

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 !=.

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 !=.

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 !=.

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 !=.

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 !=.

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 !=.

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 !=.

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 !=.

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) -> Self::Anchor

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