takeLast.d.ts 1.73 KB
import { MonoTypeOperatorFunction } from '../types';
/**
 * Emits only the last `count` values emitted by the source Observable.
 *
 * <span class="informal">Remembers the latest `count` values, then emits those
 * only when the source completes.</span>
 *
 * ![](takeLast.png)
 *
 * `takeLast` returns an Observable that emits at most the last `count` values
 * emitted by the source Observable. If the source emits fewer than `count`
 * values then all of its values are emitted. This operator must wait until the
 * `complete` notification emission from the source in order to emit the `next`
 * values on the output Observable, because otherwise it is impossible to know
 * whether or not more values will be emitted on the source. For this reason,
 * all values are emitted synchronously, followed by the complete notification.
 *
 * ## Example
 * Take the last 3 values of an Observable with many values
 * ```ts
 * import { range } from 'rxjs';
 * import { takeLast } from 'rxjs/operators';
 *
 * const many = range(1, 100);
 * const lastThree = many.pipe(takeLast(3));
 * lastThree.subscribe(x => console.log(x));
 * ```
 *
 * @see {@link take}
 * @see {@link takeUntil}
 * @see {@link takeWhile}
 * @see {@link skip}
 *
 * @throws {ArgumentOutOfRangeError} When using `takeLast(i)`, it delivers an
 * ArgumentOutOrRangeError to the Observer's `error` callback if `i < 0`.
 *
 * @param {number} count The maximum number of values to emit from the end of
 * the sequence of values emitted by the source Observable.
 * @return {Observable<T>} An Observable that emits at most the last count
 * values emitted by the source Observable.
 * @method takeLast
 * @owner Observable
 */
export declare function takeLast<T>(count: number): MonoTypeOperatorFunction<T>;