es6/Observable.js
import { root } from './util/root';
import { toSubscriber } from './util/toSubscriber';
import { observable as Symbol_observable } from './symbol/observable';
import { pipeFromArray } from './util/pipe';
/**
* A representation of any set of values over any amount of time. This is the most basic building block
* of RxJS.
*
* @class Observable<T>
*/
export class Observable {
/**
* @constructor
* @param {Function} subscribe the function that is called when the Observable is
* initially subscribed to. This function is given a Subscriber, to which new values
* can be `next`ed, or an `error` method can be called to raise an error, or
* `complete` can be called to notify of a successful completion.
*/
constructor(subscribe) {
this._isScalar = false;
if (subscribe) {
this._subscribe = subscribe;
}
}
/**
* Creates a new Observable, with this Observable as the source, and the passed
* operator defined as the new observable's operator.
* @method lift
* @param {Operator} operator the operator defining the operation to take on the observable
* @return {Observable} a new observable with the Operator applied
*/
lift(operator) {
const observable = new Observable();
observable.source = this;
observable.operator = operator;
return observable;
}
/**
* Invokes an execution of an Observable and registers Observer handlers for notifications it will emit.
*
* <span class="informal">Use it when you have all these Observables, but still nothing is happening.</span>
*
* `subscribe` is not a regular operator, but a method that calls Observable's internal `subscribe` function. It
* might be for example a function that you passed to a {@link create} static factory, but most of the time it is
* a library implementation, which defines what and when will be emitted by an Observable. This means that calling
* `subscribe` is actually the moment when Observable starts its work, not when it is created, as it is often
* thought.
*
* Apart from starting the execution of an Observable, this method allows you to listen for values
* that an Observable emits, as well as for when it completes or errors. You can achieve this in two
* following ways.
*
* The first way is creating an object that implements {@link Observer} interface. It should have methods
* defined by that interface, but note that it should be just a regular JavaScript object, which you can create
* yourself in any way you want (ES6 class, classic function constructor, object literal etc.). In particular do
* not attempt to use any RxJS implementation details to create Observers - you don't need them. Remember also
* that your object does not have to implement all methods. If you find yourself creating a method that doesn't
* do anything, you can simply omit it. Note however, that if `error` method is not provided, all errors will
* be left uncaught.
*
* The second way is to give up on Observer object altogether and simply provide callback functions in place of its methods.
* This means you can provide three functions as arguments to `subscribe`, where first function is equivalent
* of a `next` method, second of an `error` method and third of a `complete` method. Just as in case of Observer,
* if you do not need to listen for something, you can omit a function, preferably by passing `undefined` or `null`,
* since `subscribe` recognizes these functions by where they were placed in function call. When it comes
* to `error` function, just as before, if not provided, errors emitted by an Observable will be thrown.
*
* Whatever style of calling `subscribe` you use, in both cases it returns a Subscription object.
* This object allows you to call `unsubscribe` on it, which in turn will stop work that an Observable does and will clean
* up all resources that an Observable used. Note that cancelling a subscription will not call `complete` callback
* provided to `subscribe` function, which is reserved for a regular completion signal that comes from an Observable.
*
* Remember that callbacks provided to `subscribe` are not guaranteed to be called asynchronously.
* It is an Observable itself that decides when these functions will be called. For example {@link of}
* by default emits all its values synchronously. Always check documentation for how given Observable
* will behave when subscribed and if its default behavior can be modified with a {@link Scheduler}.
*
* @example <caption>Subscribe with an Observer</caption>
* const sumObserver = {
* sum: 0,
* next(value) {
* console.log('Adding: ' + value);
* this.sum = this.sum + value;
* },
* error() { // We actually could just remove this method,
* }, // since we do not really care about errors right now.
* complete() {
* console.log('Sum equals: ' + this.sum);
* }
* };
*
* Rx.Observable.of(1, 2, 3) // Synchronously emits 1, 2, 3 and then completes.
* .subscribe(sumObserver);
*
* // Logs:
* // "Adding: 1"
* // "Adding: 2"
* // "Adding: 3"
* // "Sum equals: 6"
*
*
* @example <caption>Subscribe with functions</caption>
* let sum = 0;
*
* Rx.Observable.of(1, 2, 3)
* .subscribe(
* function(value) {
* console.log('Adding: ' + value);
* sum = sum + value;
* },
* undefined,
* function() {
* console.log('Sum equals: ' + sum);
* }
* );
*
* // Logs:
* // "Adding: 1"
* // "Adding: 2"
* // "Adding: 3"
* // "Sum equals: 6"
*
*
* @example <caption>Cancel a subscription</caption>
* const subscription = Rx.Observable.interval(1000).subscribe(
* num => console.log(num),
* undefined,
* () => console.log('completed!') // Will not be called, even
* ); // when cancelling subscription
*
*
* setTimeout(() => {
* subscription.unsubscribe();
* console.log('unsubscribed!');
* }, 2500);
*
* // Logs:
* // 0 after 1s
* // 1 after 2s
* // "unsubscribed!" after 2.5s
*
*
* @param {Observer|Function} observerOrNext (optional) Either an observer with methods to be called,
* or the first of three possible handlers, which is the handler for each value emitted from the subscribed
* Observable.
* @param {Function} error (optional) A handler for a terminal event resulting from an error. If no error handler is provided,
* the error will be thrown as unhandled.
* @param {Function} complete (optional) A handler for a terminal event resulting from successful completion.
* @return {ISubscription} a subscription reference to the registered handlers
* @method subscribe
*/
subscribe(observerOrNext, error, complete) {
const { operator } = this;
const sink = toSubscriber(observerOrNext, error, complete);
if (operator) {
operator.call(sink, this.source);
}
else {
sink.add(this.source || !sink.syncErrorThrowable ? this._subscribe(sink) : this._trySubscribe(sink));
}
if (sink.syncErrorThrowable) {
sink.syncErrorThrowable = false;
if (sink.syncErrorThrown) {
throw sink.syncErrorValue;
}
}
return sink;
}
_trySubscribe(sink) {
try {
return this._subscribe(sink);
}
catch (err) {
sink.syncErrorThrown = true;
sink.syncErrorValue = err;
sink.error(err);
}
}
/**
* @method forEach
* @param {Function} next a handler for each value emitted by the observable
* @param {PromiseConstructor} [PromiseCtor] a constructor function used to instantiate the Promise
* @return {Promise} a promise that either resolves on observable completion or
* rejects with the handled error
*/
forEach(next, PromiseCtor) {
if (!PromiseCtor) {
if (root.Rx && root.Rx.config && root.Rx.config.Promise) {
PromiseCtor = root.Rx.config.Promise;
}
else if (root.Promise) {
PromiseCtor = root.Promise;
}
}
if (!PromiseCtor) {
throw new Error('no Promise impl found');
}
return new PromiseCtor((resolve, reject) => {
// Must be declared in a separate statement to avoid a RefernceError when
// accessing subscription below in the closure due to Temporal Dead Zone.
let subscription;
subscription = this.subscribe((value) => {
if (subscription) {
// if there is a subscription, then we can surmise
// the next handling is asynchronous. Any errors thrown
// need to be rejected explicitly and unsubscribe must be
// called manually
try {
next(value);
}
catch (err) {
reject(err);
subscription.unsubscribe();
}
}
else {
// if there is NO subscription, then we're getting a nexted
// value synchronously during subscription. We can just call it.
// If it errors, Observable's `subscribe` will ensure the
// unsubscription logic is called, then synchronously rethrow the error.
// After that, Promise will trap the error and send it
// down the rejection path.
next(value);
}
}, reject, resolve);
});
}
_subscribe(subscriber) {
return this.source.subscribe(subscriber);
}
/**
* An interop point defined by the es7-observable spec https://github.com/zenparsing/es-observable
* @method Symbol.observable
* @return {Observable} this instance of the observable
*/
[Symbol_observable]() {
return this;
}
/* tslint:enable:max-line-length */
/**
* Used to stitch together functional operators into a chain.
* @method pipe
* @return {Observable} the Observable result of all of the operators having
* been called in the order they were passed in.
*
* @example
*
* import { map, filter, scan } from 'rxjs/operators';
*
* Rx.Observable.interval(1000)
* .pipe(
* filter(x => x % 2 === 0),
* map(x => x + x),
* scan((acc, x) => acc + x)
* )
* .subscribe(x => console.log(x))
*/
pipe(...operations) {
if (operations.length === 0) {
return this;
}
return pipeFromArray(operations)(this);
}
/* tslint:enable:max-line-length */
toPromise(PromiseCtor) {
if (!PromiseCtor) {
if (root.Rx && root.Rx.config && root.Rx.config.Promise) {
PromiseCtor = root.Rx.config.Promise;
}
else if (root.Promise) {
PromiseCtor = root.Promise;
}
}
if (!PromiseCtor) {
throw new Error('no Promise impl found');
}
return new PromiseCtor((resolve, reject) => {
let value;
this.subscribe((x) => value = x, (err) => reject(err), () => resolve(value));
});
}
}
// HACK: Since TypeScript inherits static properties too, we have to
// fight against TypeScript here so Subject can have a different static create signature
/**
* Creates a new cold Observable by calling the Observable constructor
* @static true
* @owner Observable
* @method create
* @param {Function} subscribe? the subscriber function to be passed to the Observable constructor
* @return {Observable} a new cold observable
*/
Observable.create = (subscribe) => {
return new Observable(subscribe);
};
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