`share`

Multicasts a stream to multiple subscribers, sharing a single subscription to the source.

Functions

Creates a shared stream. The source subscription starts when the first observer subscribes and ends when the last unsubscribes.

function share<T extends Signal>(): Operator<T, T>

shareReplay

Like share, but replays the last N values to new subscribers.

function shareReplay<T extends Signal>(bufferSize?: number): Operator<T, T>

Example

import { keyboard } from "cereb";
import { share } from "cereb/operators";

const keyboard$ = keyboard(window).pipe(share());

// Single native event listener, multiple observers
keyboard$.on(handler1);
keyboard$.on(handler2);
keyboard$.on(handler3);

Use Cases

// Without share: 3 addEventListener calls
const kb1$ = keyboard(window);
const kb2$ = keyboard(window);
const kb3$ = keyboard(window);

// With share: 1 addEventListener call
const shared$ = keyboard(window).pipe(share());
shared$.on(handler1);
shared$.on(handler2);
shared$.on(handler3);

Replay Last Value

const position$ = singlePointer(element)
  .pipe(shareReplay(1));

// New subscribers immediately get the last position
position$.on(updateUI);

setTimeout(() => {
  position$.on(lateSubscriber); // Gets last position immediately
}, 1000);

Note

Many built-in stream factories like keyboard(), wheel() already use sharing internally per EventTarget.

share