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- /* @prettier */
- import { SchedulerLike } from '../types';
- import { Observable } from '../Observable';
- import { bindCallbackInternals } from './bindCallbackInternals';
- export function bindCallback(
- callbackFunc: (...args: any[]) => void,
- resultSelector: (...args: any[]) => any,
- scheduler?: SchedulerLike
- ): (...args: any[]) => Observable<any>;
- // args is the arguments array and we push the callback on the rest tuple since the rest parameter must be last (only item) in a parameter list
- export function bindCallback<A extends readonly unknown[], R extends readonly unknown[]>(
- callbackFunc: (...args: [...A, (...res: R) => void]) => void,
- schedulerLike?: SchedulerLike
- ): (...arg: A) => Observable<R extends [] ? void : R extends [any] ? R[0] : R>;
- /**
- * Converts a callback API to a function that returns an Observable.
- *
- * <span class="informal">Give it a function `f` of type `f(x, callback)` and
- * it will return a function `g` that when called as `g(x)` will output an
- * Observable.</span>
- *
- * `bindCallback` is not an operator because its input and output are not
- * Observables. The input is a function `func` with some parameters. The
- * last parameter must be a callback function that `func` calls when it is
- * done.
- *
- * The output of `bindCallback` is a function that takes the same parameters
- * as `func`, except the last one (the callback). When the output function
- * is called with arguments it will return an Observable. If function `func`
- * calls its callback with one argument, the Observable will emit that value.
- * If on the other hand the callback is called with multiple values the resulting
- * Observable will emit an array with said values as arguments.
- *
- * It is **very important** to remember that input function `func` is not called
- * when the output function is, but rather when the Observable returned by the output
- * function is subscribed. This means if `func` makes an AJAX request, that request
- * will be made every time someone subscribes to the resulting Observable, but not before.
- *
- * The last optional parameter - `scheduler` - can be used to control when the call
- * to `func` happens after someone subscribes to Observable, as well as when results
- * passed to callback will be emitted. By default, the subscription to an Observable calls `func`
- * synchronously, but using {@link asyncScheduler} as the last parameter will defer the call to `func`,
- * just like wrapping the call in `setTimeout` with a timeout of `0` would. If you were to use the async Scheduler
- * and call `subscribe` on the output Observable, all function calls that are currently executing
- * will end before `func` is invoked.
- *
- * By default, results passed to the callback are emitted immediately after `func` invokes the callback.
- * In particular, if the callback is called synchronously, then the subscription of the resulting Observable
- * will call the `next` function synchronously as well. If you want to defer that call,
- * you may use {@link asyncScheduler} just as before. This means that by using `Scheduler.async` you can
- * ensure that `func` always calls its callback asynchronously, thus avoiding terrifying Zalgo.
- *
- * Note that the Observable created by the output function will always emit a single value
- * and then complete immediately. If `func` calls the callback multiple times, values from subsequent
- * calls will not appear in the stream. If you need to listen for multiple calls,
- * you probably want to use {@link fromEvent} or {@link fromEventPattern} instead.
- *
- * If `func` depends on some context (`this` property) and is not already bound, the context of `func`
- * will be the context that the output function has at call time. In particular, if `func`
- * is called as a method of some object and if `func` is not already bound, in order to preserve the context
- * it is recommended that the context of the output function is set to that object as well.
- *
- * If the input function calls its callback in the "node style" (i.e. first argument to callback is
- * optional error parameter signaling whether the call failed or not), {@link bindNodeCallback}
- * provides convenient error handling and probably is a better choice.
- * `bindCallback` will treat such functions the same as any other and error parameters
- * (whether passed or not) will always be interpreted as regular callback argument.
- *
- * ## Examples
- *
- * Convert jQuery's getJSON to an Observable API
- *
- * ```ts
- * import { bindCallback } from 'rxjs';
- * import * as jQuery from 'jquery';
- *
- * // Suppose we have jQuery.getJSON('/my/url', callback)
- * const getJSONAsObservable = bindCallback(jQuery.getJSON);
- * const result = getJSONAsObservable('/my/url');
- * result.subscribe(x => console.log(x), e => console.error(e));
- * ```
- *
- * Receive an array of arguments passed to a callback
- *
- * ```ts
- * import { bindCallback } from 'rxjs';
- *
- * const someFunction = (n, s, cb) => {
- * cb(n, s, { someProperty: 'someValue' });
- * };
- *
- * const boundSomeFunction = bindCallback(someFunction);
- * boundSomeFunction(5, 'some string').subscribe((values) => {
- * console.log(values); // [5, 'some string', {someProperty: 'someValue'}]
- * });
- * ```
- *
- * Compare behaviour with and without `asyncScheduler`
- *
- * ```ts
- * import { bindCallback, asyncScheduler } from 'rxjs';
- *
- * function iCallMyCallbackSynchronously(cb) {
- * cb();
- * }
- *
- * const boundSyncFn = bindCallback(iCallMyCallbackSynchronously);
- * const boundAsyncFn = bindCallback(iCallMyCallbackSynchronously, null, asyncScheduler);
- *
- * boundSyncFn().subscribe(() => console.log('I was sync!'));
- * boundAsyncFn().subscribe(() => console.log('I was async!'));
- * console.log('This happened...');
- *
- * // Logs:
- * // I was sync!
- * // This happened...
- * // I was async!
- * ```
- *
- * Use `bindCallback` on an object method
- *
- * ```ts
- * import { bindCallback } from 'rxjs';
- *
- * const boundMethod = bindCallback(someObject.methodWithCallback);
- * boundMethod
- * .call(someObject) // make sure methodWithCallback has access to someObject
- * .subscribe(subscriber);
- * ```
- *
- * @see {@link bindNodeCallback}
- * @see {@link from}
- *
- * @param callbackFunc A function with a callback as the last parameter.
- * @param resultSelector A mapping function used to transform callback events.
- * @param scheduler The scheduler on which to schedule the callbacks.
- * @return A function which returns the Observable that delivers the same
- * values the callback would deliver.
- */
- export function bindCallback(
- callbackFunc: (...args: [...any[], (...res: any) => void]) => void,
- resultSelector?: ((...args: any[]) => any) | SchedulerLike,
- scheduler?: SchedulerLike
- ): (...args: any[]) => Observable<unknown> {
- return bindCallbackInternals(false, callbackFunc, resultSelector, scheduler);
- }
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