[][src]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[src]

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

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[src]

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

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[src]

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

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.

MDN documentation

impl Promise[src]

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

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

MDN documentation

impl Promise[src]

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

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[src]

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

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[src]

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

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[src]

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

Same as then, only with both arguments provided.

impl Promise[src]

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

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[src]

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

MDN documentation

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

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[src]

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[src]

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

MDN documentation

pub fn to_locale_string(&self) -> JsString[src]

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[src]

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

MDN documentation

pub fn value_of(&self) -> Object[src]

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

MDN documentation

Methods from Deref<Target = JsValue>

pub const NULL: JsValue[src]

pub const UNDEFINED: JsValue[src]

pub const TRUE: JsValue[src]

pub const FALSE: JsValue[src]

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

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[src]

Tests whether this JS value is a JS string.

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

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>[src]

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[src]

Tests whether this JS value is null

pub fn is_undefined(&self) -> bool[src]

Tests whether this JS value is undefined

pub fn is_symbol(&self) -> bool[src]

Tests whether the type of this JS value is symbol

pub fn is_object(&self) -> bool[src]

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

pub fn is_function(&self) -> bool[src]

Tests whether the type of this JS value is function.

pub fn is_truthy(&self) -> bool[src]

Tests whether the value is "truthy".

pub fn is_falsy(&self) -> bool[src]

Tests whether the value is "falsy".

Trait Implementations

impl AsRef<JsValue> for Promise[src]

impl AsRef<Object> for Promise[src]

impl AsRef<Promise> for Promise[src]

impl Clone for Promise[src]

impl Debug for Promise[src]

impl Deref for Promise[src]

type Target = Object

The resulting type after dereferencing.

impl From<JsValue> for Promise[src]

impl From<Promise> for JsValue[src]

impl From<Promise> for Object[src]

impl FromWasmAbi for Promise[src]

type Abi = <JsValue as FromWasmAbi>::Abi

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

impl IntoWasmAbi for Promise[src]

type Abi = <JsValue as IntoWasmAbi>::Abi

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

impl<'a> IntoWasmAbi for &'a Promise[src]

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

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

impl JsCast for Promise[src]

impl OptionFromWasmAbi for Promise[src]

impl OptionIntoWasmAbi for Promise[src]

impl<'a> OptionIntoWasmAbi for &'a Promise[src]

impl RefFromWasmAbi for Promise[src]

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. Read more

impl WasmDescribe for Promise[src]

Auto Trait Implementations

impl RefUnwindSafe for Promise[src]

impl !Send for Promise[src]

impl !Sync for Promise[src]

impl Unpin for Promise[src]

impl UnwindSafe for Promise[src]

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized
[src]

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T> ReturnWasmAbi for T where
    T: IntoWasmAbi
[src]

type Abi = <T as IntoWasmAbi>::Abi

Same as IntoWasmAbi::Abi

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.