@reactivex/rxjs
Version:
Reactive Extensions for modern JavaScript
164 lines • 6.58 kB
JavaScript
import { ArrayObservable } from '../observable/ArrayObservable';
import { isArray } from '../util/isArray';
import { isScheduler } from '../util/isScheduler';
import { OuterSubscriber } from '../OuterSubscriber';
import { subscribeToResult } from '../util/subscribeToResult';
/**
* Combines multiple Observables to create an Observable whose values are
* calculated from the latest values of each of its input Observables.
*
* <span class="informal">Whenever any input Observable emits a value, it
* computes a formula using the latest values from all the inputs, then emits
* the output of that formula.</span>
*
* <img src="./img/combineLatest.png" width="100%">
*
* `combineLatest` combines the values from this Observable with values from
* Observables passed as arguments. This is done by subscribing to each
* Observable, in order, and collecting an array of each of the most recent
* values any time any of the input Observables emits, then either taking that
* array and passing it as arguments to an optional `project` function and
* emitting the return value of that, or just emitting the array of recent
* values directly if there is no `project` function.
*
* @example <caption>Dynamically calculate the Body-Mass Index from an Observable of weight and one for height</caption>
* var weight = Rx.Observable.of(70, 72, 76, 79, 75);
* var height = Rx.Observable.of(1.76, 1.77, 1.78);
* var bmi = weight.combineLatest(height, (w, h) => w / (h * h));
* bmi.subscribe(x => console.log('BMI is ' + x));
*
* @see {@link combineAll}
* @see {@link merge}
* @see {@link withLatestFrom}
*
* @param {Observable} other An input Observable to combine with the source
* Observable. More than one input Observables may be given as argument.
* @param {function} [project] An optional function to project the values from
* the combined latest values into a new value on the output Observable.
* @return {Observable} An Observable of projected values from the most recent
* values from each input Observable, or an array of the most recent values from
* each input Observable.
* @method combineLatest
* @owner Observable
*/
export function combineLatest(...observables) {
let project = null;
if (typeof observables[observables.length - 1] === 'function') {
project = observables.pop();
}
// if the first and only other argument besides the resultSelector is an array
// assume it's been called with `combineLatest([obs1, obs2, obs3], project)`
if (observables.length === 1 && isArray(observables[0])) {
observables = observables[0];
}
observables.unshift(this);
return new ArrayObservable(observables).lift(new CombineLatestOperator(project));
}
/* tslint:enable:max-line-length */
/**
* Combines the values from observables passed as arguments. This is done by subscribing
* to each observable, in order, and collecting an array of each of the most recent values any time any of the observables
* emits, then either taking that array and passing it as arguments to an option `project` function and emitting the return
* value of that, or just emitting the array of recent values directly if there is no `project` function.
* @param {...Observable} observables the observables to combine
* @param {function} [project] an optional function to project the values from the combined recent values into a new value for emission.
* @return {Observable} an observable of other projected values from the most recent values from each observable, or an array of each of
* the most recent values from each observable.
* @static true
* @name combineLatest
* @owner Observable
*/
export function combineLatestStatic(...observables) {
let project = null;
let scheduler = null;
if (isScheduler(observables[observables.length - 1])) {
scheduler = observables.pop();
}
if (typeof observables[observables.length - 1] === 'function') {
project = observables.pop();
}
// if the first and only other argument besides the resultSelector is an array
// assume it's been called with `combineLatest([obs1, obs2, obs3], project)`
if (observables.length === 1 && isArray(observables[0])) {
observables = observables[0];
}
return new ArrayObservable(observables, scheduler).lift(new CombineLatestOperator(project));
}
export class CombineLatestOperator {
constructor(project) {
this.project = project;
}
call(subscriber, source) {
return source._subscribe(new CombineLatestSubscriber(subscriber, this.project));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
export class CombineLatestSubscriber extends OuterSubscriber {
constructor(destination, project) {
super(destination);
this.project = project;
this.active = 0;
this.values = [];
this.observables = [];
this.toRespond = [];
}
_next(observable) {
const toRespond = this.toRespond;
toRespond.push(toRespond.length);
this.observables.push(observable);
}
_complete() {
const observables = this.observables;
const len = observables.length;
if (len === 0) {
this.destination.complete();
}
else {
this.active = len;
for (let i = 0; i < len; i++) {
const observable = observables[i];
this.add(subscribeToResult(this, observable, observable, i));
}
}
}
notifyComplete(unused) {
if ((this.active -= 1) === 0) {
this.destination.complete();
}
}
notifyNext(outerValue, innerValue, outerIndex, innerIndex, innerSub) {
const values = this.values;
values[outerIndex] = innerValue;
const toRespond = this.toRespond;
if (toRespond.length > 0) {
const found = toRespond.indexOf(outerIndex);
if (found !== -1) {
toRespond.splice(found, 1);
}
}
if (toRespond.length === 0) {
if (this.project) {
this._tryProject(values);
}
else {
this.destination.next(values);
}
}
}
_tryProject(values) {
let result;
try {
result = this.project.apply(this, values);
}
catch (err) {
this.destination.error(err);
return;
}
this.destination.next(result);
}
}
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