Struct Promise 

#[repr(transparent)]
pub struct Promise<T = JsValue> {
    pub obj: Object,
    pub generics: PhantomData<fn() -> (T,)>,
}

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

MDN documentation

Fields

obj: Object

generics: PhantomData<fn() -> (T,)>

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 new_typed<T: Promising + JsGeneric>( cb: &mut dyn FnMut(Function<fn(T) -> Undefined>, Function<fn(JsValue) -> Undefined>), ) -> Promise<<T as Promising>::Resolution>

where dyn FnMut(Function<fn(T) -> Undefined>, Function<fn(JsValue) -> Undefined>): ErasableGenericBorrowMut<dyn FnMut(Function<fn(JsValue) -> Undefined>, Function<fn(JsValue) -> Undefined>)>, for<'__wry_bindgen> &'__wry_bindgen mut dyn FnMut(Function<fn(T) -> Undefined>, Function<fn(JsValue) -> Undefined>): EncodeTypeDef + BinaryEncode, Promise<<T as Promising>::Resolution>: ErasableGenericOwn<Promise<<JsValue as Promising>::Resolution>> + EncodeTypeDef + BatchableResult,

Creates a new Promise with the provided executor cb

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 all_iterable<I>( obj: &I, ) -> Promise<Array<<I::Item as Promising>::Resolution>>

where I::Item: Promising, I: ErasableGenericBorrow<JsValue> + EncodeTypeDef + Iterable, for<'__wry_bindgen> &'__wry_bindgen I: BinaryEncode, Promise<Array<<I::Item as Promising>::Resolution>>: ErasableGenericOwn<Promise<Array<<JsValue as Promising>::Resolution>>> + EncodeTypeDef + BatchableResult,

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 all_settled(obj: &JsValue) -> Promise

The Promise.allSettled(iterable) method returns a single Promise that resolves when all of the promises in the iterable argument have either fulfilled or rejected or when the iterable argument contains no promises.

MDN documentation

impl Promise

pub fn all_settled_iterable<I>( obj: &I, ) -> Promise<Array<PromiseState<<I::Item as Promising>::Resolution>>>

where I::Item: Promising, I: ErasableGenericBorrow<JsValue> + EncodeTypeDef + Iterable, for<'__wry_bindgen> &'__wry_bindgen I: BinaryEncode, Promise<Array<PromiseState<<I::Item as Promising>::Resolution>>>: ErasableGenericOwn<Promise<Array<PromiseState<<JsValue as Promising>::Resolution>>>> + EncodeTypeDef + BatchableResult,

The Promise.allSettled(iterable) method returns a single Promise that resolves when all of the promises in the iterable argument have either fulfilled or rejected or when the iterable argument contains no promises.

MDN documentation

impl Promise

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

The Promise.any(iterable) method returns a single Promise that resolves when any of the promises in the iterable argument have resolved or when the iterable argument contains no promises. It rejects with an AggregateError if all promises in the iterable rejected.

MDN documentation

impl Promise

pub fn any_iterable<I>(obj: &I) -> Promise<<I::Item as Promising>::Resolution>

where I::Item: Promising, I: ErasableGenericBorrow<JsValue> + EncodeTypeDef + Iterable, for<'__wry_bindgen> &'__wry_bindgen I: BinaryEncode, Promise<<I::Item as Promising>::Resolution>: ErasableGenericOwn<Promise<<JsValue as Promising>::Resolution>> + EncodeTypeDef + BatchableResult,

The Promise.any(iterable) method returns a single Promise that resolves when any of the promises in the iterable argument have resolved or when the iterable argument contains no promises. It rejects with an AggregateError if all promises in the iterable rejected.

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.

MDN documentation

impl Promise

pub fn race_iterable<I>(obj: &I) -> Promise<<I::Item as Promising>::Resolution>

where I::Item: Promising, I: ErasableGenericBorrow<JsValue> + EncodeTypeDef + Iterable, for<'__wry_bindgen> &'__wry_bindgen I: BinaryEncode, Promise<<I::Item as Promising>::Resolution>: ErasableGenericOwn<Promise<<JsValue as Promising>::Resolution>> + EncodeTypeDef + BatchableResult,

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

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

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

MDN documentation

impl<T> Promise<T>

pub fn reject_typed(obj: &JsValue) -> Promise<T>

where Promise<T>: ErasableGenericOwn<Promise<JsValue>> + EncodeTypeDef + BatchableResult,

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

MDN documentation

impl Promise

pub fn resolve<U>(obj: &U) -> Promise<U::Resolution>

where U: ErasableGenericBorrow<JsValue> + EncodeTypeDef + Promising, for<'__wry_bindgen> &'__wry_bindgen U: BinaryEncode, Promise<U::Resolution>: ErasableGenericOwn<Promise<JsValue>> + EncodeTypeDef + BatchableResult,

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<T> Promise<T>

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

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<T> Promise<T>

pub fn catch_map<'a, R: Promising>( &self, cb: &ScopedClosure<'a, dyn FnMut(T) -> Result<R, JsError>>, ) -> Promise<R::Resolution>

where ScopedClosure<'a, dyn FnMut(T) -> Result<R, JsError>>: ErasableGenericBorrow<ScopedClosure<'static, dyn FnMut(JsValue) -> Result<JsValue, JsError>>>, Promise<R::Resolution>: ErasableGenericOwn<Promise<JsValue>> + EncodeTypeDef + BatchableResult,

Same as catch, but returning a result to become the new Promise value.

impl<T> Promise<T>

pub fn then<'a>(&self, cb: &ScopedClosure<'a, dyn FnMut(T)>) -> Promise<JsValue>

where ScopedClosure<'a, dyn FnMut(T)>: ErasableGenericBorrow<ScopedClosure<'static, dyn FnMut(JsValue)>>,

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<T> Promise<T>

pub fn then_with_reject<'a, R: Promising>( &self, resolve: &ScopedClosure<'a, dyn FnMut(T) -> Result<R, JsError>>, reject: &ScopedClosure<'a, dyn FnMut(JsValue) -> Result<R, JsError>>, ) -> Promise<R::Resolution>

where ScopedClosure<'a, dyn FnMut(T) -> Result<R, JsError>>: ErasableGenericBorrow<ScopedClosure<'static, dyn FnMut(JsValue) -> Result<JsValue, JsError>>>, ScopedClosure<'a, dyn FnMut(JsValue) -> Result<R, JsError>>: ErasableGenericBorrow<ScopedClosure<'static, dyn FnMut(JsValue) -> Result<JsValue, JsError>>>, Promise<R::Resolution>: ErasableGenericOwn<Promise<JsValue>> + EncodeTypeDef + BatchableResult,

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<T> Promise<T>

pub fn then_map<'a, R: Promising>( &self, cb: &ScopedClosure<'a, dyn FnMut(T) -> Result<R, JsError>>, ) -> Promise<R::Resolution>

where ScopedClosure<'a, dyn FnMut(T) -> Result<R, JsError>>: ErasableGenericBorrow<ScopedClosure<'static, dyn FnMut(JsValue) -> Result<JsValue, JsError>>>, Promise<R::Resolution>: ErasableGenericOwn<Promise<JsValue>> + EncodeTypeDef + BatchableResult,

Alias for then() with a return value. 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: &ScopedClosure<'_, dyn FnMut(JsValue)>, reject: &ScopedClosure<'_, dyn FnMut(JsValue)>, ) -> Promise

Same as then, only with both arguments provided.

MDN documentation

impl<T> Promise<T>

pub fn finally(&self, cb: &ScopedClosure<'_, dyn FnMut()>) -> Promise<JsValue>

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

impl Promise

pub fn all_tuple<T: PromiseTuple>(promises: T) -> Promise<T::Joined>

Heterogeneous counterpart to Promise::all_iterable: accepts a Rust tuple of Promise<T_i> and returns a single Promise resolving to a typed ArrayTuple<(T_1, T_2, ..., T_n)>.

Destructure the awaited result via ArrayTuple::into_tuple to get the individual values back as a native Rust tuple. Implemented for arity 1..=8.

Rejects with the first rejection, matching Promise.all semantics.

Example

use js_sys::Promise;

let (response, buffer) = Promise::all_tuple((fetch_promise, buffer_promise))
    .await?
    .into_tuple();

pub fn all_settled_tuple<T: PromiseTuple>(promises: T) -> Promise<T::Settled>

Heterogeneous counterpart to Promise::all_settled_iterable: accepts a Rust tuple of Promise<T_i> and returns a single Promise resolving to a typed ArrayTuple<(PromiseState<T_1>, ..., PromiseState<T_n>)>.

Unlike Promise::all_tuple, this never rejects early: every input settles (fulfills or rejects) and is reflected by its PromiseState slot in the result tuple. Implemented for arity 1..=8.

Example

use js_sys::Promise;

let results = Promise::all_settled_tuple((fetch_promise, buffer_promise)).await?;
let (response_state, buffer_state) = results.into_tuple();

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.

MDN documentation

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

👎Deprecated:

Use Object::hasOwn instead.

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 to_js_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 id(&self) -> u64

Get the heap ID for this value.

This is used internally for encoding values to send to JS.

pub fn unchecked_into_f64(&self) -> f64

Returns the value as f64 without type checking. Used by serde-wasm-bindgen for numeric conversions.

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

where T: JsCast,

Check if this value is an instance of a specific JS type.

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

Checked division.

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

Power operation.

pub fn bit_and(&self, rhs: &JsValue) -> JsValue

Bitwise AND.

pub fn bit_or(&self, rhs: &JsValue) -> JsValue

Bitwise OR.

pub fn bit_xor(&self, rhs: &JsValue) -> JsValue

Bitwise XOR.

pub fn bit_not(&self) -> JsValue

Bitwise NOT.

pub fn shl(&self, rhs: &JsValue) -> JsValue

Left shift.

pub fn shr(&self, rhs: &JsValue) -> JsValue

Signed right shift.

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

Unsigned right shift.

pub fn add(&self, rhs: &JsValue) -> JsValue

Add.

pub fn sub(&self, rhs: &JsValue) -> JsValue

Subtract.

pub fn mul(&self, rhs: &JsValue) -> JsValue

Multiply.

pub fn div(&self, rhs: &JsValue) -> JsValue

Divide.

pub fn rem(&self, rhs: &JsValue) -> JsValue

Remainder.

pub fn neg(&self) -> JsValue

Negate.

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

Less than comparison.

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

Less than or equal comparison.

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

Greater than comparison.

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

Greater than or equal comparison.

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

Loose equality (==).

pub fn is_falsy(&self) -> bool

Check if this value is a falsy value in JavaScript.

pub fn is_truthy(&self) -> bool

Check if this value is a truthy value in JavaScript.

pub fn is_object(&self) -> bool

Check if this value is an object.

pub fn is_function(&self) -> bool

Check if this value is a function.

pub fn is_string(&self) -> bool

Check if this value is a string.

pub fn is_symbol(&self) -> bool

Check if this value is a symbol.

pub fn is_bigint(&self) -> bool

Check if this value is a bigint.

pub fn is_array(&self) -> bool

Check if this value is an Array.

pub fn is_undefined(&self) -> bool

Check if this value is undefined.

pub fn is_null(&self) -> bool

Check if this value is null.

pub fn is_null_or_undefined(&self) -> bool

Check if this value is null or undefined.

pub fn js_typeof(&self) -> JsValue

Get the typeof this value as a string.

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

Check if this value has a property with the given name.

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

Get the value as a bool.

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

Get the value as an f64.

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

Get the value as a string.

pub fn as_debug_string(&self) -> String

Get a debug string representation of the value.

Trait Implementations

impl<T> AsRef<JsValue> for Promise<T>

fn as_ref(&self) -> &JsValue

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

impl<T> AsRef<Object> for Promise<T>

fn as_ref(&self) -> &Object

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

impl<T> AsRef<Promise<T>> for Promise<T>

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

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

impl<T> BatchableResult for Promise<T>

fn try_placeholder(batch: &mut Runtime) -> Option<Self>

Returns Some(placeholder) for opaque types that can be batched, None for types that require flushing to get the actual value.

impl<T> BinaryDecode for Promise<T>

fn decode(decoder: &mut DecodedData<'_>) -> Result<Self, DecodeError>

impl<T> BinaryEncode for Promise<T>

fn encode(self, encoder: &mut EncodedData)

impl<T: Clone> Clone for Promise<T>

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

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for Promise<T>

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

Formats the value using the given formatter.

impl<T> Deref for Promise<T>

type Target = Object

The resulting type after dereferencing.

fn deref(&self) -> &Object

Dereferences the value.

impl<T> EncodeTypeDef for Promise<T>

fn encode_type_def(buf: &mut Vec<u8>)

Encode this type’s definition into the buffer. For primitives, this is just the TypeTag byte. For callbacks, this includes param count, param types, and return type.

impl<T> ErasableGeneric for Promise<T>

type Repr = JsValue

impl<T> From<JsValue> for Promise<T>

fn from(val: JsValue) -> Self

Converts to this type from the input type.

impl<T: FromWasmAbi + 'static> From<Promise<T>> for JsFuture<T>

fn from(js: Promise<T>) -> JsFuture<T>

Converts to this type from the input type.

impl<T> From<Promise<T>> for JsValue

fn from(val: Promise<T>) -> Self

Converts to this type from the input type.

impl<T> From<Promise<T>> for Object

fn from(val: Promise<T>) -> Object

Converts to this type from the input type.

impl<T: FromWasmAbi + 'static> IntoFuture for Promise<T>

type Output = Result<T, JsValue>

The output that the future will produce on completion.

type IntoFuture = JsFuture<T>

Which kind of future are we turning this into?

fn into_future(self) -> JsFuture<T>

Creates a future from a value.

impl<T: 'static> IntoJsGeneric for Promise<T>

where Promise<T>: JsGeneric,

type JsCanon = Promise<T>

fn to_js(self) -> Self::JsCanon

impl<T> JsCast for Promise<T>

fn instanceof(__val: &JsValue) -> bool

Check if a JsValue is an instance of this type.

fn unchecked_from_js(val: JsValue) -> Self

Unchecked cast from JsValue to this type.

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

Unchecked cast from a JsValue reference to a reference of this type.

fn is_type_of(val: &JsValue) -> bool

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

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,

Try to cast this value to type T.

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

where T: JsCast,

Try to get a reference to type T from this value.

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

where T: JsCast,

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

fn unchecked_into<T>(self) -> T

where T: JsCast,

Unchecked cast to another type.

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

where T: JsCast,

Unchecked cast to a reference of another type.

impl<T: JsGeneric> Promising for Promise<T>

type Resolution = T

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

impl<T> UpcastFrom<Promise<T>> for JsOption<Object>

impl<T, __WryUpcastTarget0> UpcastFrom<Promise<T>> for JsOption<Promise<__WryUpcastTarget0>>

where __WryUpcastTarget0: UpcastFrom<T>,

impl<T> UpcastFrom<Promise<T>> for JsValue

impl<T> UpcastFrom<Promise<T>> for Object

impl<T, __WryUpcastTarget0> UpcastFrom<Promise<T>> for Promise<__WryUpcastTarget0>

where __WryUpcastTarget0: UpcastFrom<T>,