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CancellablePromise.ts
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CancellablePromise.ts
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import { Cancellation } from './Cancellation';
import { noop } from './noop';
/**
* The most abstract thing we can cancel — a thenable with a cancel method.
*/
export type PromiseWithCancel<T> = PromiseLike<T> & { cancel(): void };
/**
* Determines if an arbitrary value is a thenable with a cancel method.
*/
export function isPromiseWithCancel<T>(
value: unknown
): value is PromiseWithCancel<T> {
return (
typeof value === 'object' &&
typeof (value as { then?: unknown }).then === 'function' &&
typeof (value as { cancel?: unknown }).cancel === 'function'
);
}
/**
* A promise with a `cancel` method.
*
* If canceled, the `CancellablePromise` will reject with a [[`Cancellation`]]
* object.
*
* @typeParam T what the `CancellablePromise` resolves to
*/
export class CancellablePromise<T> {
/**
* As a consumer of the library, you shouldn't ever need to access
* `CancellablePromise.promise` directly.
*
* If you are subclassing `CancellablePromise` for some reason, you
* can access this property.
*/
protected readonly promise: Promise<T>;
// IMPORTANT: When defining a new `cancel` function,
// e.g. in the implementation of `then`,
// always use an arrow function so that `this` is bound.
/**
* Cancel the `CancellablePromise`.
*/
readonly cancel: (reason?: string) => void;
/**
* @param promise a normal promise or thenable
* @param cancel a function that cancels `promise`. **Calling `cancel` after
* `promise` has resolved must be a no-op.**
*/
constructor(promise: PromiseLike<T>, cancel: (reason?: string) => void) {
this.promise = Promise.resolve(promise);
this.cancel = cancel;
}
/**
* Analogous to `Promise.then`.
*
* `onFulfilled` on `onRejected` can return a value, a normal promise, or a
* `CancellablePromise`. So you can make a chain a `CancellablePromise`s
* like this:
*
* ```
* const overallPromise = cancellableAsyncFunction1()
* .then(cancellableAsyncFunction2)
* .then(cancellableAsyncFunction3)
* .then(cancellableAsyncFunction4)
* ```
*
* Then if you call `overallPromise.cancel`, `cancel` is called on all
* `CancellablePromise`s in the chain! In practice, this means that
* whichever async operation is in progress will be canceled.
*
* @returns a new CancellablePromise
*/
then<TResult1 = T, TResult2 = never>(
onFulfilled?:
| ((value: T) => TResult1 | PromiseLike<TResult1>)
| undefined
| null,
onRejected?:
| ((reason: any) => TResult2 | PromiseLike<TResult2>) // eslint-disable-line @typescript-eslint/no-explicit-any -- to match the types used for Promise in the official lib.d.ts
| undefined
| null
): CancellablePromise<TResult1 | TResult2> {
let fulfill;
let reject;
let callbackPromiseWithCancel: PromiseWithCancel<unknown> | undefined;
if (onFulfilled) {
fulfill = (value: T): TResult1 | PromiseLike<TResult1> => {
const nextValue: TResult1 | PromiseLike<TResult1> = onFulfilled(value);
if (isPromiseWithCancel(nextValue))
callbackPromiseWithCancel = nextValue;
return nextValue;
};
}
if (onRejected) {
reject = (reason: unknown): TResult2 | PromiseLike<TResult2> => {
const nextValue: TResult2 | PromiseLike<TResult2> = onRejected(reason);
if (isPromiseWithCancel(nextValue))
callbackPromiseWithCancel = nextValue;
return nextValue;
};
}
const newPromise = this.promise.then(fulfill, reject);
const newCancel = () => {
this.cancel();
callbackPromiseWithCancel?.cancel();
};
return new CancellablePromise(newPromise, newCancel);
}
/* eslint-disable @typescript-eslint/no-explicit-any -- to match the types used for Promise in the official lib.d.ts */
/**
* Analogous to `Promise.catch`.
*/
catch<TResult = never>(
onRejected?:
| ((reason: any) => TResult | PromiseLike<TResult>)
| undefined
| null
): CancellablePromise<T | TResult> {
return this.then(undefined, onRejected);
}
/* eslint-enable @typescript-eslint/no-explicit-any */
/**
* Attaches a callback that is invoked when the Promise is settled
* (fulfilled or rejected). The resolved value cannot be modified from the
* callback.
* @param onFinally The callback to execute when the Promise is settled
* (fulfilled or rejected).
* @returns A Promise for the completion of the callback.
*/
finally(onFinally?: (() => void) | undefined | null): CancellablePromise<T> {
return new CancellablePromise(this.promise.finally(onFinally), this.cancel);
}
/**
* This is necessary to make `CancellablePromise` assignable to `Promise`.
*/
// eslint-disable-next-line class-methods-use-this
get [Symbol.toStringTag](): string {
return 'CancellablePromise';
}
/**
* Analogous to `Promise.resolve`.
*
* The returned promise should resolve even if it is canceled. The idea is
* that the promise is resolved instantaneously, so by the time the promise
* is canceled, it has already resolved.
*/
static resolve(): CancellablePromise<void>;
static resolve<T>(value: T): CancellablePromise<T>;
static resolve(value?: unknown): CancellablePromise<unknown> {
return new CancellablePromise(Promise.resolve(value), noop);
}
/**
* Analogous to `Promise.reject`.
*
* Like `CancellablePromise.resolve`, canceling the returned
* `CancellablePromise` is a no-op.
*
* @param reason this should probably be an `Error` object
*/
static reject<T>(reason?: unknown): CancellablePromise<T> {
return new CancellablePromise(Promise.reject(reason), noop);
}
/**
* Analogous to `Promise.all`.
*
* @param values an array that may contain `CancellablePromise`s, promises,
* thenables, and resolved values
* @returns a [[`CancellablePromise`]], which, if canceled, will cancel each
* of the promises passed in to `CancellablePromise.all`.
*/
static all<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10>(
values: readonly [
T1 | PromiseLike<T1>,
T2 | PromiseLike<T2>,
T3 | PromiseLike<T3>,
T4 | PromiseLike<T4>,
T5 | PromiseLike<T5>,
T6 | PromiseLike<T6>,
T7 | PromiseLike<T7>,
T8 | PromiseLike<T8>,
T9 | PromiseLike<T9>,
T10 | PromiseLike<T10>
]
): CancellablePromise<[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10]>;
/**
* Analogous to `Promise.all`.
*
* @param values an array that may contain `CancellablePromise`s, promises,
* thenables, and resolved values
* @returns a [[`CancellablePromise`]], which, if canceled, will cancel each
* of the promises passed in to `CancellablePromise.all`.
*/
static all<T1, T2, T3, T4, T5, T6, T7, T8, T9>(
values: readonly [
T1 | PromiseLike<T1>,
T2 | PromiseLike<T2>,
T3 | PromiseLike<T3>,
T4 | PromiseLike<T4>,
T5 | PromiseLike<T5>,
T6 | PromiseLike<T6>,
T7 | PromiseLike<T7>,
T8 | PromiseLike<T8>,
T9 | PromiseLike<T9>
]
): CancellablePromise<[T1, T2, T3, T4, T5, T6, T7, T8, T9]>;
/**
* Analogous to `Promise.all`.
*
* @param values an array that may contain `CancellablePromise`s, promises,
* thenables, and resolved values
* @returns a [[`CancellablePromise`]], which, if canceled, will cancel each
* of the promises passed in to `CancellablePromise.all`.
*/
static all<T1, T2, T3, T4, T5, T6, T7, T8>(
values: readonly [
T1 | PromiseLike<T1>,
T2 | PromiseLike<T2>,
T3 | PromiseLike<T3>,
T4 | PromiseLike<T4>,
T5 | PromiseLike<T5>,
T6 | PromiseLike<T6>,
T7 | PromiseLike<T7>,
T8 | PromiseLike<T8>
]
): CancellablePromise<[T1, T2, T3, T4, T5, T6, T7, T8]>;
/**
* Analogous to `Promise.all`.
*
* @param values an array that may contain `CancellablePromise`s, promises,
* thenables, and resolved values
* @returns a [[`CancellablePromise`]], which, if canceled, will cancel each
* of the promises passed in to `CancellablePromise.all`.
*/
static all<T1, T2, T3, T4, T5, T6, T7>(
values: readonly [
T1 | PromiseLike<T1>,
T2 | PromiseLike<T2>,
T3 | PromiseLike<T3>,
T4 | PromiseLike<T4>,
T5 | PromiseLike<T5>,
T6 | PromiseLike<T6>,
T7 | PromiseLike<T7>
]
): CancellablePromise<[T1, T2, T3, T4, T5, T6, T7]>;
/**
* Analogous to `Promise.all`.
*
* @param values an array that may contain `CancellablePromise`s, promises,
* thenables, and resolved values
* @returns a [[`CancellablePromise`]], which, if canceled, will cancel each
* of the promises passed in to `CancellablePromise.all`.
*/
static all<T1, T2, T3, T4, T5, T6>(
values: readonly [
T1 | PromiseLike<T1>,
T2 | PromiseLike<T2>,
T3 | PromiseLike<T3>,
T4 | PromiseLike<T4>,
T5 | PromiseLike<T5>,
T6 | PromiseLike<T6>
]
): CancellablePromise<[T1, T2, T3, T4, T5, T6]>;
/**
* Analogous to `Promise.all`.
*
* @param values an array that may contain `CancellablePromise`s, promises,
* thenables, and resolved values
* @returns a [[`CancellablePromise`]], which, if canceled, will cancel each
* of the promises passed in to `CancellablePromise.all`.
*/
static all<T1, T2, T3, T4, T5>(
values: readonly [
T1 | PromiseLike<T1>,
T2 | PromiseLike<T2>,
T3 | PromiseLike<T3>,
T4 | PromiseLike<T4>,
T5 | PromiseLike<T5>
]
): CancellablePromise<[T1, T2, T3, T4, T5]>;
/**
* Analogous to `Promise.all`.
*
* @param values an array that may contain `CancellablePromise`s, promises,
* thenables, and resolved values
* @returns a [[`CancellablePromise`]], which, if canceled, will cancel each
* of the promises passed in to `CancellablePromise.all`.
*/
static all<T1, T2, T3, T4>(
values: readonly [
T1 | PromiseLike<T1>,
T2 | PromiseLike<T2>,
T3 | PromiseLike<T3>,
T4 | PromiseLike<T4>
]
): CancellablePromise<[T1, T2, T3, T4]>;
/**
* Analogous to `Promise.all`.
*
* @param values an array that may contain `CancellablePromise`s, promises,
* thenables, and resolved values
* @returns a [[`CancellablePromise`]], which, if canceled, will cancel each
* of the promises passed in to `CancellablePromise.all`.
*/
static all<T1, T2, T3>(
values: readonly [
T1 | PromiseLike<T1>,
T2 | PromiseLike<T2>,
T3 | PromiseLike<T3>
]
): CancellablePromise<[T1, T2, T3]>;
/**
* Analogous to `Promise.all`.
*
* @param values an array that may contain `CancellablePromise`s, promises,
* thenables, and resolved values
* @returns a [[`CancellablePromise`]], which, if canceled, will cancel each
* of the promises passed in to `CancellablePromise.all`.
*/
static all<T1, T2>(
values: readonly [T1 | PromiseLike<T1>, T2 | PromiseLike<T2>]
): CancellablePromise<[T1, T2]>;
/**
* Analogous to `Promise.all`.
*
* @param values an array that may contain `CancellablePromise`s, promises,
* thenables, and resolved values
* @returns a [[`CancellablePromise`]], which, if canceled, will cancel each
* of the promises passed in to `CancellablePromise.all`.
*/
static all<T>(
values: readonly (T | PromiseLike<T>)[]
): CancellablePromise<T[]>;
/**
* Analogous to `Promise.all`.
*
* @param values an array that may contain `CancellablePromise`s, promises,
* thenables, and resolved values
* @returns a [[`CancellablePromise`]], which, if canceled, will cancel each
* of the promises passed in to `CancellablePromise.all`.
*/
static all(values: readonly unknown[]): CancellablePromise<unknown> {
return new CancellablePromise(Promise.all(values), () => {
for (const value of values) {
if (isPromiseWithCancel(value)) value.cancel();
}
});
}
/**
* Creates a `CancellablePromise` that is resolved with an array of results
* when all of the provided `Promises` resolve or reject.
* @param values An array of `Promises`.
* @returns A new `CancellablePromise`.
*/
static allSettled<T extends readonly unknown[] | readonly [unknown]>(
values: T
): CancellablePromise<{
-readonly [P in keyof T]: PromiseSettledResult<
T[P] extends PromiseLike<infer U> ? U : T[P]
>;
}>;
/**
* Creates a `CancellablePromise` that is resolved with an array of results
* when all of the provided `Promise`s resolve or reject.
*
* @param values An array of `Promise`s.
* @returns A new `CancellablePromise`. Canceling it cancels all of the input
* promises.
*/
static allSettled<T>(
values: Iterable<T>
): CancellablePromise<
PromiseSettledResult<T extends PromiseLike<infer U> ? U : T>[]
>;
static allSettled(values: unknown[]): CancellablePromise<unknown> {
const cancel = (): void => {
for (const value of values) {
if (isPromiseWithCancel(value)) {
value.cancel();
}
}
};
return new CancellablePromise(Promise.allSettled(values), cancel);
}
/**
* Creates a `CancellablePromise` that is resolved or rejected when any of
* the provided `Promises` are resolved or rejected.
* @param values An array of `Promises`.
* @returns A new `CancellablePromise`. Canceling it cancels all of the input
* promises.
*/
static race<T extends readonly unknown[] | []>(
values: T
): CancellablePromise<Awaited<T[number]>> {
const cancel = (): void => {
for (const value of values) {
if (isPromiseWithCancel(value)) {
value.cancel();
}
}
};
return new CancellablePromise(Promise.race(values), cancel);
}
// Promise.any is an ES2021 feature. Not yet implemented.
// /**
// * The any function returns a `CancellablePromise` that is fulfilled by the
// * first given promise to be fulfilled, or rejected with an `AggregateError`
// * containing an array of rejection reasons if all of the given promises are
// * rejected. It resolves all elements of the passed iterable to promises as
// * it runs this algorithm.
// * @param values An array or iterable of Promises.
// * @returns A new `CancellablePromise`.
// */
// any<T>(values: (T | PromiseLike<T>)[] | Iterable<T | PromiseLike<T>>): CancellablePromise<T> {
// return new CancellablePromise(Promise.any(values), cancel))
// }
/**
* @returns a `CancellablePromise` that resolves after `ms` milliseconds.
*/
static delay(ms: number): CancellablePromise<void> {
let timer: NodeJS.Timer | undefined;
let rejectFn: (reason?: unknown) => void = noop;
const promise = new Promise<void>((resolve, reject) => {
timer = setTimeout(() => {
resolve();
rejectFn = noop;
}, ms);
rejectFn = reject;
});
return new CancellablePromise(promise, () => {
if (timer) clearTimeout(timer);
rejectFn(new Cancellation());
});
}
}