242 lines
11 KiB
JavaScript
242 lines
11 KiB
JavaScript
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import { Observable } from '../Observable';
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import { tryCatch } from '../util/tryCatch';
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import { errorObject } from '../util/errorObject';
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import { AsyncSubject } from '../AsyncSubject';
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/**
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* We need this JSDoc comment for affecting ESDoc.
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* @extends {Ignored}
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* @hide true
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*/
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export class BoundCallbackObservable extends Observable {
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constructor(callbackFunc, selector, args, context, scheduler) {
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super();
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this.callbackFunc = callbackFunc;
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this.selector = selector;
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this.args = args;
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this.context = context;
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this.scheduler = scheduler;
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}
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/* tslint:enable:max-line-length */
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/**
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* Converts a callback API to a function that returns an Observable.
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*
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* <span class="informal">Give it a function `f` of type `f(x, callback)` and
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* it will return a function `g` that when called as `g(x)` will output an
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* Observable.</span>
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*
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* `bindCallback` is not an operator because its input and output are not
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* Observables. The input is a function `func` with some parameters, the
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* last parameter must be a callback function that `func` calls when it is
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* done.
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*
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* The output of `bindCallback` is a function that takes the same parameters
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* as `func`, except the last one (the callback). When the output function
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* is called with arguments it will return an Observable. If function `func`
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* calls its callback with one argument the Observable will emit that value.
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* If on the other hand the callback is called with multiple values the resulting
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* Observable will emit an array with said values as arguments.
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*
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* It is very important to remember that input function `func` is not called
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* when the output function is, but rather when the Observable returned by the output
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* function is subscribed. This means if `func` makes an AJAX request, that request
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* will be made every time someone subscribes to the resulting Observable, but not before.
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*
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* Optionally, a selector function can be passed to `bindObservable`. The selector function
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* takes the same arguments as the callback and returns the value that will be emitted by the Observable.
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* Even though by default multiple arguments passed to callback appear in the stream as an array
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* the selector function will be called with arguments directly, just as the callback would.
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* This means you can imagine the default selector (when one is not provided explicitly)
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* as a function that aggregates all its arguments into an array, or simply returns first argument
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* if there is only one.
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*
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* The last optional parameter - {@link Scheduler} - can be used to control when the call
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* to `func` happens after someone subscribes to Observable, as well as when results
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* passed to callback will be emitted. By default, the subscription to an Observable calls `func`
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* synchronously, but using `Scheduler.async` as the last parameter will defer the call to `func`,
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* just like wrapping the call in `setTimeout` with a timeout of `0` would. If you use the async Scheduler
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* and call `subscribe` on the output Observable all function calls that are currently executing
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* will end before `func` is invoked.
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*
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* By default results passed to the callback are emitted immediately after `func` invokes the callback.
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* In particular, if the callback is called synchronously the subscription of the resulting Observable
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* will call the `next` function synchronously as well. If you want to defer that call,
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* you may use `Scheduler.async` just as before. This means that by using `Scheduler.async` you can
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* ensure that `func` always calls its callback asynchronously, thus avoiding terrifying Zalgo.
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*
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* Note that the Observable created by the output function will always emit a single value
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* and then complete immediately. If `func` calls the callback multiple times, values from subsequent
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* calls will not appear in the stream. If you need to listen for multiple calls,
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* you probably want to use {@link fromEvent} or {@link fromEventPattern} instead.
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*
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* If `func` depends on some context (`this` property) and is not already bound the context of `func`
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* will be the context that the output function has at call time. In particular, if `func`
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* is called as a method of some objec and if `func` is not already bound, in order to preserve the context
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* it is recommended that the context of the output function is set to that object as well.
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*
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* If the input function calls its callback in the "node style" (i.e. first argument to callback is
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* optional error parameter signaling whether the call failed or not), {@link bindNodeCallback}
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* provides convenient error handling and probably is a better choice.
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* `bindCallback` will treat such functions the same as any other and error parameters
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* (whether passed or not) will always be interpreted as regular callback argument.
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*
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*
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* @example <caption>Convert jQuery's getJSON to an Observable API</caption>
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* // Suppose we have jQuery.getJSON('/my/url', callback)
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* var getJSONAsObservable = Rx.Observable.bindCallback(jQuery.getJSON);
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* var result = getJSONAsObservable('/my/url');
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* result.subscribe(x => console.log(x), e => console.error(e));
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*
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*
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* @example <caption>Receive an array of arguments passed to a callback</caption>
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* someFunction((a, b, c) => {
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* console.log(a); // 5
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* console.log(b); // 'some string'
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* console.log(c); // {someProperty: 'someValue'}
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* });
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*
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* const boundSomeFunction = Rx.Observable.bindCallback(someFunction);
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* boundSomeFunction().subscribe(values => {
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* console.log(values) // [5, 'some string', {someProperty: 'someValue'}]
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* });
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*
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*
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* @example <caption>Use bindCallback with a selector function</caption>
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* someFunction((a, b, c) => {
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* console.log(a); // 'a'
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* console.log(b); // 'b'
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* console.log(c); // 'c'
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* });
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*
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* const boundSomeFunction = Rx.Observable.bindCallback(someFunction, (a, b, c) => a + b + c);
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* boundSomeFunction().subscribe(value => {
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* console.log(value) // 'abc'
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* });
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*
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*
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* @example <caption>Compare behaviour with and without async Scheduler</caption>
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* function iCallMyCallbackSynchronously(cb) {
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* cb();
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* }
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*
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* const boundSyncFn = Rx.Observable.bindCallback(iCallMyCallbackSynchronously);
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* const boundAsyncFn = Rx.Observable.bindCallback(iCallMyCallbackSynchronously, null, Rx.Scheduler.async);
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*
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* boundSyncFn().subscribe(() => console.log('I was sync!'));
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* boundAsyncFn().subscribe(() => console.log('I was async!'));
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* console.log('This happened...');
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*
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* // Logs:
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* // I was sync!
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* // This happened...
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* // I was async!
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*
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*
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* @example <caption>Use bindCallback on an object method</caption>
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* const boundMethod = Rx.Observable.bindCallback(someObject.methodWithCallback);
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* boundMethod.call(someObject) // make sure methodWithCallback has access to someObject
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* .subscribe(subscriber);
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*
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*
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* @see {@link bindNodeCallback}
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* @see {@link from}
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* @see {@link fromPromise}
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*
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* @param {function} func A function with a callback as the last parameter.
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* @param {function} [selector] A function which takes the arguments from the
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* callback and maps them to a value that is emitted on the output Observable.
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* @param {Scheduler} [scheduler] The scheduler on which to schedule the
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* callbacks.
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* @return {function(...params: *): Observable} A function which returns the
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* Observable that delivers the same values the callback would deliver.
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* @static true
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* @name bindCallback
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* @owner Observable
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*/
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static create(func, selector = undefined, scheduler) {
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return function (...args) {
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return new BoundCallbackObservable(func, selector, args, this, scheduler);
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};
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}
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/** @deprecated internal use only */ _subscribe(subscriber) {
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const callbackFunc = this.callbackFunc;
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const args = this.args;
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const scheduler = this.scheduler;
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let subject = this.subject;
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if (!scheduler) {
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if (!subject) {
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subject = this.subject = new AsyncSubject();
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const handler = function handlerFn(...innerArgs) {
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const source = handlerFn.source;
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const { selector, subject } = source;
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if (selector) {
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const result = tryCatch(selector).apply(this, innerArgs);
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if (result === errorObject) {
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subject.error(errorObject.e);
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}
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else {
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subject.next(result);
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subject.complete();
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}
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}
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else {
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subject.next(innerArgs.length <= 1 ? innerArgs[0] : innerArgs);
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subject.complete();
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}
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};
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// use named function instance to avoid closure.
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handler.source = this;
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const result = tryCatch(callbackFunc).apply(this.context, args.concat(handler));
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if (result === errorObject) {
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subject.error(errorObject.e);
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}
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}
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return subject.subscribe(subscriber);
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}
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else {
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return scheduler.schedule(BoundCallbackObservable.dispatch, 0, { source: this, subscriber, context: this.context });
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}
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}
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static dispatch(state) {
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const self = this;
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const { source, subscriber, context } = state;
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const { callbackFunc, args, scheduler } = source;
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let subject = source.subject;
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if (!subject) {
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subject = source.subject = new AsyncSubject();
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const handler = function handlerFn(...innerArgs) {
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const source = handlerFn.source;
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const { selector, subject } = source;
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if (selector) {
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const result = tryCatch(selector).apply(this, innerArgs);
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if (result === errorObject) {
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self.add(scheduler.schedule(dispatchError, 0, { err: errorObject.e, subject }));
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}
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else {
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self.add(scheduler.schedule(dispatchNext, 0, { value: result, subject }));
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}
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}
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else {
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const value = innerArgs.length <= 1 ? innerArgs[0] : innerArgs;
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self.add(scheduler.schedule(dispatchNext, 0, { value, subject }));
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}
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};
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// use named function to pass values in without closure
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handler.source = source;
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const result = tryCatch(callbackFunc).apply(context, args.concat(handler));
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if (result === errorObject) {
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subject.error(errorObject.e);
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}
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}
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self.add(subject.subscribe(subscriber));
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}
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}
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function dispatchNext(arg) {
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const { value, subject } = arg;
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subject.next(value);
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subject.complete();
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}
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function dispatchError(arg) {
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const { err, subject } = arg;
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subject.error(err);
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}
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//# sourceMappingURL=BoundCallbackObservable.js.map
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