work.suroh.tk/node_modules/rxjs/_esm2015/operators/startWith.js

42 lines
1.6 KiB
JavaScript

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) {
return (source) => {
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), source);
}
else if (len > 1) {
return concatStatic(new ArrayObservable(array, scheduler), source);
}
else {
return concatStatic(new EmptyObservable(scheduler), source);
}
};
}
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