W3cubDocs

/RxJS

bufferCount

function stable

Buffers the source Observable values until the size hits the maximum bufferSize given.

`bufferCount<T>(bufferSize: number, startBufferEvery: number = null): OperatorFunction<T, T[]>`

Parameters

bufferSize

The maximum size of the buffer emitted.

startBufferEvery

Optional. Default is null.

Interval at which to start a new buffer. For example if startBufferEvery is 2, then a new buffer will be started on every other value from the source. A new buffer is started at the beginning of the source by default.

Returns

OperatorFunction<T, T[]>: An Observable of arrays of buffered values.

Description

Collects values from the past as an array, and emits that array only when its size reaches bufferSize.

bufferCount marble diagram

Buffers a number of values from the source Observable by bufferSize then emits the buffer and clears it, and starts a new buffer each startBufferEvery values. If startBufferEvery is not provided or is null, then new buffers are started immediately at the start of the source and when each buffer closes and is emitted.

Examples

Emit the last two click events as an array

import { fromEvent } from 'rxjs';
import { bufferCount } from 'rxjs/operators';

const clicks = fromEvent(document, 'click');
const buffered = clicks.pipe(bufferCount(2));
buffered.subscribe(x => console.log(x));

On every click, emit the last two click events as an array

import { fromEvent } from 'rxjs';
import { bufferCount } from 'rxjs/operators';

const clicks = fromEvent(document, 'click');
const buffered = clicks.pipe(bufferCount(2, 1));
buffered.subscribe(x => console.log(x));