es6/observable/concat.js

import { isScheduler } from '../util/isScheduler';
import { of } from './of';
import { from } from './from';
import { concatAll } from '../operators/concatAll';
/* tslint:enable:max-line-length */
/**
 * Creates an output Observable which sequentially emits all values from given
 * Observable and then moves on to the next.
 *
 * <span class="informal">Concatenates multiple Observables together by
 * sequentially emitting their values, one Observable after the other.</span>
 *
 * <img src="./img/concat.png" width="100%">
 *
 * `concat` joins multiple Observables together, by subscribing to them one at a time and
 * merging their results into the output Observable. You can pass either an array of
 * Observables, or put them directly as arguments. Passing an empty array will result
 * in Observable that completes immediately.
 *
 * `concat` will subscribe to first input Observable and emit all its values, without
 * changing or affecting them in any way. When that Observable completes, it will
 * subscribe to then next Observable passed and, again, emit its values. This will be
 * repeated, until the operator runs out of Observables. When last input Observable completes,
 * `concat` will complete as well. At any given moment only one Observable passed to operator
 * emits values. If you would like to emit values from passed Observables concurrently, check out
 * {@link merge} instead, especially with optional `concurrent` parameter. As a matter of fact,
 * `concat` is an equivalent of `merge` operator with `concurrent` parameter set to `1`.
 *
 * Note that if some input Observable never completes, `concat` will also never complete
 * and Observables following the one that did not complete will never be subscribed. On the other
 * hand, if some Observable simply completes immediately after it is subscribed, it will be
 * invisible for `concat`, which will just move on to the next Observable.
 *
 * If any Observable in chain errors, instead of passing control to the next Observable,
 * `concat` will error immediately as well. Observables that would be subscribed after
 * the one that emitted error, never will.
 *
 * If you pass to `concat` the same Observable many times, its stream of values
 * will be "replayed" on every subscription, which means you can repeat given Observable
 * as many times as you like. If passing the same Observable to `concat` 1000 times becomes tedious,
 * you can always use {@link repeat}.
 *
 * @example <caption>Concatenate a timer counting from 0 to 3 with a synchronous sequence from 1 to 10</caption>
 * var timer = Rx.Observable.interval(1000).take(4);
 * var sequence = Rx.Observable.range(1, 10);
 * var result = Rx.Observable.concat(timer, sequence);
 * result.subscribe(x => console.log(x));
 *
 * // results in:
 * // 0 -1000ms-> 1 -1000ms-> 2 -1000ms-> 3 -immediate-> 1 ... 10
 *
 *
 * @example <caption>Concatenate an array of 3 Observables</caption>
 * var timer1 = Rx.Observable.interval(1000).take(10);
 * var timer2 = Rx.Observable.interval(2000).take(6);
 * var timer3 = Rx.Observable.interval(500).take(10);
 * var result = Rx.Observable.concat([timer1, timer2, timer3]); // note that array is passed
 * result.subscribe(x => console.log(x));
 *
 * // results in the following:
 * // (Prints to console sequentially)
 * // -1000ms-> 0 -1000ms-> 1 -1000ms-> ... 9
 * // -2000ms-> 0 -2000ms-> 1 -2000ms-> ... 5
 * // -500ms-> 0 -500ms-> 1 -500ms-> ... 9
 *
 *
 * @example <caption>Concatenate the same Observable to repeat it</caption>
 * const timer = Rx.Observable.interval(1000).take(2);
 *
 * Rx.Observable.concat(timer, timer) // concating the same Observable!
 * .subscribe(
 *   value => console.log(value),
 *   err => {},
 *   () => console.log('...and it is done!')
 * );
 *
 * // Logs:
 * // 0 after 1s
 * // 1 after 2s
 * // 0 after 3s
 * // 1 after 4s
 * // "...and it is done!" also after 4s
 *
 * @see {@link concatAll}
 * @see {@link concatMap}
 * @see {@link concatMapTo}
 *
 * @param {ObservableInput} input1 An input Observable to concatenate with others.
 * @param {ObservableInput} input2 An input Observable to concatenate with others.
 * More than one input Observables may be given as argument.
 * @param {Scheduler} [scheduler=null] An optional IScheduler to schedule each
 * Observable subscription on.
 * @return {Observable} All values of each passed Observable merged into a
 * single Observable, in order, in serial fashion.
 * @static true
 * @name concat
 * @owner Observable
 */
export function concat(...observables) {
    if (observables.length === 1 || (observables.length === 2 && isScheduler(observables[1]))) {
        return from(observables[0]);
    }
    return concatAll()(of(...observables));
}
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