es6/operator/startWith.js

import { ArrayObservable } from '../observable/ArrayObservable';
import { ScalarObservable } from '../observable/ScalarObservable';
import { EmptyObservable } from '../observable/EmptyObservable';
import { concat as concatStatic } from '../observable/concat';
import { isScheduler } from '../util/isScheduler';
/* tslint:enable:max-line-length */
/**
 * Returns an Observable that emits the items you specify as arguments before it begins to emit
 * items emitted by the source Observable.
 *
 * <img src="./img/startWith.png" width="100%">
 *
 * @param {...T} values - Items you want the modified Observable to emit first.
 * @param {Scheduler} [scheduler] - A {@link IScheduler} to use for scheduling
 * the emissions of the `next` notifications.
 * @return {Observable} An Observable that emits the items in the specified Iterable and then emits the items
 * emitted by the source Observable.
 * @method startWith
 * @owner Observable
 */
export function startWith(...array) {
    let scheduler = array[array.length - 1];
    if (isScheduler(scheduler)) {
        array.pop();
    }
    else {
        scheduler = null;
    }
    const len = array.length;
    if (len === 1) {
        return concatStatic(new ScalarObservable(array[0], scheduler), this);
    }
    else if (len > 1) {
        return concatStatic(new ArrayObservable(array, scheduler), this);
    }
    else {
        return concatStatic(new EmptyObservable(scheduler), this);
    }
}
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