work.suroh.tk/node_modules/rxjs/_esm5/observable/combineLatest.js

136 lines
6.5 KiB
JavaScript

/** PURE_IMPORTS_START .._util_isScheduler,.._util_isArray,._ArrayObservable,.._operators_combineLatest PURE_IMPORTS_END */
import { isScheduler } from '../util/isScheduler';
import { isArray } from '../util/isArray';
import { ArrayObservable } from './ArrayObservable';
import { CombineLatestOperator } from '../operators/combineLatest';
/* tslint:enable:max-line-length */
/**
* 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 all the Observables passed as
* arguments. This is done by subscribing to each Observable in order and,
* whenever any Observable emits, collecting an array of the most recent
* values from each Observable. So if you pass `n` Observables to operator,
* returned Observable will always emit an array of `n` values, in order
* corresponding to order of passed Observables (value from the first Observable
* on the first place and so on).
*
* Static version of `combineLatest` accepts either an array of Observables
* or each Observable can be put directly as an argument. Note that array of
* Observables is good choice, if you don't know beforehand how many Observables
* you will combine. Passing empty array will result in Observable that
* completes immediately.
*
* To ensure output array has always the same length, `combineLatest` will
* actually wait for all input Observables to emit at least once,
* before it starts emitting results. This means if some Observable emits
* values before other Observables started emitting, all that values but last
* will be lost. On the other hand, is some Observable does not emit value but
* completes, resulting Observable will complete at the same moment without
* emitting anything, since it will be now impossible to include value from
* completed Observable in resulting array. Also, if some input Observable does
* not emit any value and never completes, `combineLatest` will also never emit
* and never complete, since, again, it will wait for all streams to emit some
* value.
*
* If at least one Observable was passed to `combineLatest` and all passed Observables
* emitted something, resulting Observable will complete when all combined
* streams complete. So even if some Observable completes, result of
* `combineLatest` will still emit values when other Observables do. In case
* of completed Observable, its value from now on will always be the last
* emitted value. On the other hand, if any Observable errors, `combineLatest`
* will error immediately as well, and all other Observables will be unsubscribed.
*
* `combineLatest` accepts as optional parameter `project` function, which takes
* as arguments all values that would normally be emitted by resulting Observable.
* `project` can return any kind of value, which will be then emitted by Observable
* instead of default array. Note that `project` does not take as argument that array
* of values, but values themselves. That means default `project` can be imagined
* as function that takes all its arguments and puts them into an array.
*
*
* @example <caption>Combine two timer Observables</caption>
* const firstTimer = Rx.Observable.timer(0, 1000); // emit 0, 1, 2... after every second, starting from now
* const secondTimer = Rx.Observable.timer(500, 1000); // emit 0, 1, 2... after every second, starting 0,5s from now
* const combinedTimers = Rx.Observable.combineLatest(firstTimer, secondTimer);
* combinedTimers.subscribe(value => console.log(value));
* // Logs
* // [0, 0] after 0.5s
* // [1, 0] after 1s
* // [1, 1] after 1.5s
* // [2, 1] after 2s
*
*
* @example <caption>Combine an array of Observables</caption>
* const observables = [1, 5, 10].map(
* n => Rx.Observable.of(n).delay(n * 1000).startWith(0) // emit 0 and then emit n after n seconds
* );
* const combined = Rx.Observable.combineLatest(observables);
* combined.subscribe(value => console.log(value));
* // Logs
* // [0, 0, 0] immediately
* // [1, 0, 0] after 1s
* // [1, 5, 0] after 5s
* // [1, 5, 10] after 10s
*
*
* @example <caption>Use project function to dynamically calculate the Body-Mass Index</caption>
* var weight = Rx.Observable.of(70, 72, 76, 79, 75);
* var height = Rx.Observable.of(1.76, 1.77, 1.78);
* var bmi = Rx.Observable.combineLatest(weight, height, (w, h) => w / (h * h));
* bmi.subscribe(x => console.log('BMI is ' + x));
*
* // With output to console:
* // BMI is 24.212293388429753
* // BMI is 23.93948099205209
* // BMI is 23.671253629592222
*
*
* @see {@link combineAll}
* @see {@link merge}
* @see {@link withLatestFrom}
*
* @param {ObservableInput} observable1 An input Observable to combine with other Observables.
* @param {ObservableInput} observable2 An input Observable to combine with other Observables.
* More than one input Observables may be given as arguments
* or an array of Observables may be given as the first argument.
* @param {function} [project] An optional function to project the values from
* the combined latest values into a new value on the output Observable.
* @param {Scheduler} [scheduler=null] The IScheduler to use for subscribing to
* each input 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.
* @static true
* @name combineLatest
* @owner Observable
*/
export function combineLatest() {
var observables = [];
for (var _i = 0; _i < arguments.length; _i++) {
observables[_i - 0] = arguments[_i];
}
var project = null;
var 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));
}
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