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Diffstat (limited to 'node_modules/rxjs/src/internal/observable/bindCallback.ts')
| -rw-r--r-- | node_modules/rxjs/src/internal/observable/bindCallback.ts | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/node_modules/rxjs/src/internal/observable/bindCallback.ts b/node_modules/rxjs/src/internal/observable/bindCallback.ts new file mode 100644 index 0000000..a4bd574 --- /dev/null +++ b/node_modules/rxjs/src/internal/observable/bindCallback.ts @@ -0,0 +1,149 @@ +/* @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); +} |
