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startWith.ts
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startWith.ts
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import { Observable } from '../Observable';
import { fromArray } from '../observable/fromArray';
import { scalar } from '../observable/scalar';
import { empty } from '../observable/empty';
import { concat as concatStatic } from '../observable/concat';
import { isScheduler } from '../util/isScheduler';
import { MonoTypeOperatorFunction, SchedulerLike } from '../types';
/* tslint:disable:max-line-length */
export function startWith<T>(v1: T, scheduler?: SchedulerLike): MonoTypeOperatorFunction<T>;
export function startWith<T>(v1: T, v2: T, scheduler?: SchedulerLike): MonoTypeOperatorFunction<T>;
export function startWith<T>(v1: T, v2: T, v3: T, scheduler?: SchedulerLike): MonoTypeOperatorFunction<T>;
export function startWith<T>(v1: T, v2: T, v3: T, v4: T, scheduler?: SchedulerLike): MonoTypeOperatorFunction<T>;
export function startWith<T>(v1: T, v2: T, v3: T, v4: T, v5: T, scheduler?: SchedulerLike): MonoTypeOperatorFunction<T>;
export function startWith<T>(v1: T, v2: T, v3: T, v4: T, v5: T, v6: T, scheduler?: SchedulerLike): MonoTypeOperatorFunction<T>;
export function startWith<T>(...array: Array<T | SchedulerLike>): MonoTypeOperatorFunction<T>;
/* 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.
*
* <span class="informal">First emits its arguments in order, and then any
* emissions from the source.</span>
*
* ![](startWith.png)
*
* ## Examples
*
* Start the chain of emissions with `"first"`, `"second"`
*
* ```javascript
* of("from source")
* .pipe(startWith("first", "second"))
* .subscribe(x => console.log(x));
*
* // results:
* // "first"
* // "second"
* // "from source"
* ```
*
* @param {...T} values - Items you want the modified Observable to emit first.
* @param {SchedulerLike} [scheduler] - A {@link SchedulerLike} 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<T>(...array: Array<T | SchedulerLike>): MonoTypeOperatorFunction<T> {
return (source: Observable<T>) => {
let scheduler = <SchedulerLike>array[array.length - 1];
if (isScheduler(scheduler)) {
array.pop();
} else {
scheduler = null;
}
const len = array.length;
if (len === 1 && !scheduler) {
return concatStatic(scalar(array[0] as T), source);
} else if (len > 0) {
return concatStatic(fromArray(array as T[], scheduler), source);
} else {
return concatStatic<T>(empty(scheduler) as any, source);
}
};
}