296 lines
12 KiB
JavaScript
296 lines
12 KiB
JavaScript
import { root } from './util/root';
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import { toSubscriber } from './util/toSubscriber';
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import { observable as Symbol_observable } from './symbol/observable';
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import { pipeFromArray } from './util/pipe';
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/**
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* A representation of any set of values over any amount of time. This is the most basic building block
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* of RxJS.
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*
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* @class Observable<T>
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*/
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export class Observable {
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/**
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* @constructor
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* @param {Function} subscribe the function that is called when the Observable is
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* initially subscribed to. This function is given a Subscriber, to which new values
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* can be `next`ed, or an `error` method can be called to raise an error, or
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* `complete` can be called to notify of a successful completion.
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*/
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constructor(subscribe) {
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this._isScalar = false;
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if (subscribe) {
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this._subscribe = subscribe;
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}
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}
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/**
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* Creates a new Observable, with this Observable as the source, and the passed
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* operator defined as the new observable's operator.
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* @method lift
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* @param {Operator} operator the operator defining the operation to take on the observable
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* @return {Observable} a new observable with the Operator applied
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*/
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lift(operator) {
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const observable = new Observable();
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observable.source = this;
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observable.operator = operator;
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return observable;
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}
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/**
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* Invokes an execution of an Observable and registers Observer handlers for notifications it will emit.
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*
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* <span class="informal">Use it when you have all these Observables, but still nothing is happening.</span>
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*
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* `subscribe` is not a regular operator, but a method that calls Observable's internal `subscribe` function. It
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* might be for example a function that you passed to a {@link create} static factory, but most of the time it is
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* a library implementation, which defines what and when will be emitted by an Observable. This means that calling
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* `subscribe` is actually the moment when Observable starts its work, not when it is created, as it is often
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* thought.
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*
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* Apart from starting the execution of an Observable, this method allows you to listen for values
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* that an Observable emits, as well as for when it completes or errors. You can achieve this in two
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* following ways.
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*
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* The first way is creating an object that implements {@link Observer} interface. It should have methods
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* defined by that interface, but note that it should be just a regular JavaScript object, which you can create
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* yourself in any way you want (ES6 class, classic function constructor, object literal etc.). In particular do
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* not attempt to use any RxJS implementation details to create Observers - you don't need them. Remember also
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* that your object does not have to implement all methods. If you find yourself creating a method that doesn't
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* do anything, you can simply omit it. Note however, that if `error` method is not provided, all errors will
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* be left uncaught.
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*
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* The second way is to give up on Observer object altogether and simply provide callback functions in place of its methods.
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* This means you can provide three functions as arguments to `subscribe`, where first function is equivalent
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* of a `next` method, second of an `error` method and third of a `complete` method. Just as in case of Observer,
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* if you do not need to listen for something, you can omit a function, preferably by passing `undefined` or `null`,
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* since `subscribe` recognizes these functions by where they were placed in function call. When it comes
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* to `error` function, just as before, if not provided, errors emitted by an Observable will be thrown.
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*
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* Whatever style of calling `subscribe` you use, in both cases it returns a Subscription object.
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* This object allows you to call `unsubscribe` on it, which in turn will stop work that an Observable does and will clean
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* up all resources that an Observable used. Note that cancelling a subscription will not call `complete` callback
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* provided to `subscribe` function, which is reserved for a regular completion signal that comes from an Observable.
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*
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* Remember that callbacks provided to `subscribe` are not guaranteed to be called asynchronously.
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* It is an Observable itself that decides when these functions will be called. For example {@link of}
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* by default emits all its values synchronously. Always check documentation for how given Observable
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* will behave when subscribed and if its default behavior can be modified with a {@link Scheduler}.
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*
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* @example <caption>Subscribe with an Observer</caption>
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* const sumObserver = {
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* sum: 0,
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* next(value) {
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* console.log('Adding: ' + value);
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* this.sum = this.sum + value;
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* },
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* error() { // We actually could just remove this method,
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* }, // since we do not really care about errors right now.
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* complete() {
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* console.log('Sum equals: ' + this.sum);
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* }
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* };
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*
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* Rx.Observable.of(1, 2, 3) // Synchronously emits 1, 2, 3 and then completes.
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* .subscribe(sumObserver);
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*
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* // Logs:
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* // "Adding: 1"
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* // "Adding: 2"
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* // "Adding: 3"
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* // "Sum equals: 6"
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*
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*
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* @example <caption>Subscribe with functions</caption>
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* let sum = 0;
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*
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* Rx.Observable.of(1, 2, 3)
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* .subscribe(
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* function(value) {
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* console.log('Adding: ' + value);
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* sum = sum + value;
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* },
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* undefined,
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* function() {
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* console.log('Sum equals: ' + sum);
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* }
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* );
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*
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* // Logs:
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* // "Adding: 1"
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* // "Adding: 2"
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* // "Adding: 3"
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* // "Sum equals: 6"
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*
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*
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* @example <caption>Cancel a subscription</caption>
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* const subscription = Rx.Observable.interval(1000).subscribe(
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* num => console.log(num),
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* undefined,
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* () => console.log('completed!') // Will not be called, even
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* ); // when cancelling subscription
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*
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*
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* setTimeout(() => {
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* subscription.unsubscribe();
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* console.log('unsubscribed!');
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* }, 2500);
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*
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* // Logs:
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* // 0 after 1s
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* // 1 after 2s
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* // "unsubscribed!" after 2.5s
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*
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*
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* @param {Observer|Function} observerOrNext (optional) Either an observer with methods to be called,
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* or the first of three possible handlers, which is the handler for each value emitted from the subscribed
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* Observable.
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* @param {Function} error (optional) A handler for a terminal event resulting from an error. If no error handler is provided,
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* the error will be thrown as unhandled.
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* @param {Function} complete (optional) A handler for a terminal event resulting from successful completion.
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* @return {ISubscription} a subscription reference to the registered handlers
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* @method subscribe
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*/
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subscribe(observerOrNext, error, complete) {
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const { operator } = this;
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const sink = toSubscriber(observerOrNext, error, complete);
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if (operator) {
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operator.call(sink, this.source);
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}
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else {
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sink.add(this.source || !sink.syncErrorThrowable ? this._subscribe(sink) : this._trySubscribe(sink));
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}
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if (sink.syncErrorThrowable) {
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sink.syncErrorThrowable = false;
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if (sink.syncErrorThrown) {
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throw sink.syncErrorValue;
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}
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}
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return sink;
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}
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_trySubscribe(sink) {
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try {
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return this._subscribe(sink);
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}
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catch (err) {
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sink.syncErrorThrown = true;
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sink.syncErrorValue = err;
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sink.error(err);
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}
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}
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/**
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* @method forEach
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* @param {Function} next a handler for each value emitted by the observable
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* @param {PromiseConstructor} [PromiseCtor] a constructor function used to instantiate the Promise
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* @return {Promise} a promise that either resolves on observable completion or
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* rejects with the handled error
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*/
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forEach(next, PromiseCtor) {
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if (!PromiseCtor) {
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if (root.Rx && root.Rx.config && root.Rx.config.Promise) {
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PromiseCtor = root.Rx.config.Promise;
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}
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else if (root.Promise) {
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PromiseCtor = root.Promise;
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}
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}
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if (!PromiseCtor) {
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throw new Error('no Promise impl found');
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}
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return new PromiseCtor((resolve, reject) => {
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// Must be declared in a separate statement to avoid a RefernceError when
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// accessing subscription below in the closure due to Temporal Dead Zone.
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let subscription;
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subscription = this.subscribe((value) => {
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if (subscription) {
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// if there is a subscription, then we can surmise
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// the next handling is asynchronous. Any errors thrown
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// need to be rejected explicitly and unsubscribe must be
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// called manually
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try {
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next(value);
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}
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catch (err) {
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reject(err);
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subscription.unsubscribe();
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}
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}
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else {
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// if there is NO subscription, then we're getting a nexted
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// value synchronously during subscription. We can just call it.
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// If it errors, Observable's `subscribe` will ensure the
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// unsubscription logic is called, then synchronously rethrow the error.
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// After that, Promise will trap the error and send it
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// down the rejection path.
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next(value);
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}
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}, reject, resolve);
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});
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}
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/** @deprecated internal use only */ _subscribe(subscriber) {
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return this.source.subscribe(subscriber);
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}
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/**
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* An interop point defined by the es7-observable spec https://github.com/zenparsing/es-observable
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* @method Symbol.observable
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* @return {Observable} this instance of the observable
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*/
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[Symbol_observable]() {
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return this;
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}
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/* tslint:enable:max-line-length */
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/**
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* Used to stitch together functional operators into a chain.
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* @method pipe
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* @return {Observable} the Observable result of all of the operators having
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* been called in the order they were passed in.
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*
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* @example
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*
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* import { map, filter, scan } from 'rxjs/operators';
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*
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* Rx.Observable.interval(1000)
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* .pipe(
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* filter(x => x % 2 === 0),
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* map(x => x + x),
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* scan((acc, x) => acc + x)
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* )
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* .subscribe(x => console.log(x))
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*/
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pipe(...operations) {
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if (operations.length === 0) {
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return this;
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}
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return pipeFromArray(operations)(this);
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}
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/* tslint:enable:max-line-length */
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toPromise(PromiseCtor) {
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if (!PromiseCtor) {
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if (root.Rx && root.Rx.config && root.Rx.config.Promise) {
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PromiseCtor = root.Rx.config.Promise;
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}
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else if (root.Promise) {
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PromiseCtor = root.Promise;
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}
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}
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if (!PromiseCtor) {
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throw new Error('no Promise impl found');
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}
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return new PromiseCtor((resolve, reject) => {
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let value;
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this.subscribe((x) => value = x, (err) => reject(err), () => resolve(value));
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});
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}
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}
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// HACK: Since TypeScript inherits static properties too, we have to
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// fight against TypeScript here so Subject can have a different static create signature
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/**
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* Creates a new cold Observable by calling the Observable constructor
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* @static true
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* @owner Observable
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* @method create
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* @param {Function} subscribe? the subscriber function to be passed to the Observable constructor
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* @return {Observable} a new cold observable
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*/
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Observable.create = (subscribe) => {
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return new Observable(subscribe);
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};
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//# sourceMappingURL=Observable.js.map
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