Struct js_sys::Promise

#[must_use]
#[repr(transparent)]pub struct Promise { /* fields omitted */ }

The Promise object represents the eventual completion (or failure) of an asynchronous operation, and its resulting value.

MDN documentation

Implementations

impl Promise

pub fn new(cb: &mut dyn FnMut(Function, Function)) -> Promise

Creates a new Promise with the provided executor cb

The cb is a function that is passed with the arguments resolve and reject. The cb function is executed immediately by the Promise implementation, passing resolve and reject functions (the executor is called before the Promise constructor even returns the created object). The resolve and reject functions, when called, resolve or reject the promise, respectively. The executor normally initiates some asynchronous work, and then, once that completes, either calls the resolve function to resolve the promise or else rejects it if an error occurred.

If an error is thrown in the executor function, the promise is rejected. The return value of the executor is ignored.

MDN documentation

impl Promise

pub fn all(obj: &JsValue) -> Promise

The Promise.all(iterable) method returns a single Promise that resolves when all of the promises in the iterable argument have resolved or when the iterable argument contains no promises. It rejects with the reason of the first promise that rejects.

MDN documentation

impl Promise

pub fn race(obj: &JsValue) -> Promise

The Promise.race(iterable) method returns a promise that resolves or rejects as soon as one of the promises in the iterable resolves or rejects, with the value or reason from that promise.

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impl Promise

pub fn reject(obj: &JsValue) -> Promise

The Promise.reject(reason) method returns a Promise object that is rejected with the given reason.

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impl Promise

pub fn resolve(obj: &JsValue) -> Promise

The Promise.resolve(value) method returns a Promise object that is resolved with the given value. If the value is a promise, that promise is returned; if the value is a thenable (i.e. has a “then” method), the returned promise will “follow” that thenable, adopting its eventual state; otherwise the returned promise will be fulfilled with the value.

MDN documentation

impl Promise

pub fn catch(&self, cb: &Closure<dyn FnMut(JsValue)>) -> Promise

The catch() method returns a Promise and deals with rejected cases only. It behaves the same as calling Promise.prototype.then(undefined, onRejected) (in fact, calling obj.catch(onRejected) internally calls obj.then(undefined, onRejected)).

MDN documentation

impl Promise

pub fn then(&self, cb: &Closure<dyn FnMut(JsValue)>) -> Promise

The then() method returns a Promise. It takes up to two arguments: callback functions for the success and failure cases of the Promise.

MDN documentation

impl Promise

pub fn then2(
    &self,
    resolve: &Closure<dyn FnMut(JsValue)>,
    reject: &Closure<dyn FnMut(JsValue)>
) -> Promise

Same as then, only with both arguments provided.

impl Promise

pub fn finally(&self, cb: &Closure<dyn FnMut()>) -> Promise

The finally() method returns a Promise. When the promise is settled, whether fulfilled or rejected, the specified callback function is executed. This provides a way for code that must be executed once the Promise has been dealt with to be run whether the promise was fulfilled successfully or rejected.

This lets you avoid duplicating code in both the promise’s then() and catch() handlers.

MDN documentation

Methods from Deref<Target = Object>

pub fn constructor(&self) -> Function

The constructor property returns a reference to the Object constructor function that created the instance object.

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pub fn has_own_property(&self, property: &JsValue) -> bool

The hasOwnProperty() method returns a boolean indicating whether the object has the specified property as its own property (as opposed to inheriting it).

MDN documentation

pub fn is_prototype_of(&self, value: &JsValue) -> bool

The isPrototypeOf() method checks if an object exists in another object’s prototype chain.

MDN documentation

pub fn property_is_enumerable(&self, property: &JsValue) -> bool

The propertyIsEnumerable() method returns a Boolean indicating whether the specified property is enumerable.

MDN documentation

pub fn to_locale_string(&self) -> JsString

The toLocaleString() method returns a string representing the object. This method is meant to be overridden by derived objects for locale-specific purposes.

MDN documentation

pub fn to_string(&self) -> JsString

The toString() method returns a string representing the object.

MDN documentation

pub fn value_of(&self) -> Object

The valueOf() method returns the primitive value of the specified object.

MDN documentation

Methods from Deref<Target = JsValue>

pub const NULL: JsValue

pub const UNDEFINED: JsValue

pub const TRUE: JsValue

pub const FALSE: JsValue

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 AsRef<JsValue> for Promise

fn as_ref(&self) -> &JsValue

Performs the conversion.

impl AsRef<Object> for Promise

fn as_ref(&self) -> &Object

Performs the conversion.

impl AsRef<Promise> for Promise

fn as_ref(&self) -> &Promise

Performs the conversion.

impl Clone for Promise

fn clone(&self) -> Promise

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Promise

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

Formats the value using the given formatter.

impl Deref for Promise

type Target = Object

The resulting type after dereferencing.

fn deref(&self) -> &Object

Dereferences the value.

impl From<JsValue> for Promise

fn from(obj: JsValue) -> Promise

Performs the conversion.

impl From<Promise> for JsValue

fn from(obj: Promise) -> JsValue

Performs the conversion.

impl From<Promise> for Object

fn from(obj: Promise) -> Object

Performs the conversion.

impl FromWasmAbi for Promise

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 IntoWasmAbi for Promise

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<'a> IntoWasmAbi for &'a Promise

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 JsCast for Promise

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.

pub fn has_type<T>(&self) -> bool where
    T: JsCast, 

Test whether this JS value has a type T.

pub 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.

pub 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.

pub fn unchecked_into<T>(self) -> T where
    T: JsCast, 

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

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

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

pub fn is_instance_of<T>(&self) -> bool where
    T: JsCast, 

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

pub fn is_type_of(val: &JsValue) -> bool

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

impl OptionFromWasmAbi for Promise

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 OptionIntoWasmAbi for Promise

fn none() -> Self::Abi

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

impl<'a> OptionIntoWasmAbi for &'a Promise

fn none() -> Self::Abi

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

impl RefFromWasmAbi for Promise

type Abi = <JsValue as RefFromWasmAbi>::Abi

The wasm ABI type references to Self are recovered from.

type Anchor = ManuallyDrop<Promise>

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 WasmDescribe for Promise

fn describe()