From e4fa1e69e7ebfb627c7198fd1a9881e9327ec4d4 Mon Sep 17 00:00:00 2001 From: Pinapelz Date: Sat, 28 Jun 2025 17:26:46 -0700 Subject: initial commit: scaffolding --- node_modules/rxjs/src/internal/firstValueFrom.ts | 75 ++++++++++++++++++++++++ 1 file changed, 75 insertions(+) create mode 100644 node_modules/rxjs/src/internal/firstValueFrom.ts (limited to 'node_modules/rxjs/src/internal/firstValueFrom.ts') diff --git a/node_modules/rxjs/src/internal/firstValueFrom.ts b/node_modules/rxjs/src/internal/firstValueFrom.ts new file mode 100644 index 0000000..2fc4bcf --- /dev/null +++ b/node_modules/rxjs/src/internal/firstValueFrom.ts @@ -0,0 +1,75 @@ +import { Observable } from './Observable'; +import { EmptyError } from './util/EmptyError'; +import { SafeSubscriber } from './Subscriber'; + +export interface FirstValueFromConfig { + defaultValue: T; +} + +export function firstValueFrom(source: Observable, config: FirstValueFromConfig): Promise; +export function firstValueFrom(source: Observable): Promise; + +/** + * Converts an observable to a promise by subscribing to the observable, + * and returning a promise that will resolve as soon as the first value + * arrives from the observable. The subscription will then be closed. + * + * If the observable stream completes before any values were emitted, the + * returned promise will reject with {@link EmptyError} or will resolve + * with the default value if a default was specified. + * + * If the observable stream emits an error, the returned promise will reject + * with that error. + * + * **WARNING**: Only use this with observables you *know* will emit at least one value, + * *OR* complete. If the source observable does not emit one value or complete, you will + * end up with a promise that is hung up, and potentially all of the state of an + * async function hanging out in memory. To avoid this situation, look into adding + * something like {@link timeout}, {@link take}, {@link takeWhile}, or {@link takeUntil} + * amongst others. + * + * ## Example + * + * Wait for the first value from a stream and emit it from a promise in + * an async function + * + * ```ts + * import { interval, firstValueFrom } from 'rxjs'; + * + * async function execute() { + * const source$ = interval(2000); + * const firstNumber = await firstValueFrom(source$); + * console.log(`The first number is ${ firstNumber }`); + * } + * + * execute(); + * + * // Expected output: + * // 'The first number is 0' + * ``` + * + * @see {@link lastValueFrom} + * + * @param source the observable to convert to a promise + * @param config a configuration object to define the `defaultValue` to use if the source completes without emitting a value + */ +export function firstValueFrom(source: Observable, config?: FirstValueFromConfig): Promise { + const hasConfig = typeof config === 'object'; + return new Promise((resolve, reject) => { + const subscriber = new SafeSubscriber({ + next: (value) => { + resolve(value); + subscriber.unsubscribe(); + }, + error: reject, + complete: () => { + if (hasConfig) { + resolve(config!.defaultValue); + } else { + reject(new EmptyError()); + } + }, + }); + source.subscribe(subscriber); + }); +} -- cgit v1.2.3