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Emitter

import { Emitter } from '@dr.pogodin/react-utils'; // or from '@dr.pogodin/js-utils'

The Emitter class implements a simple, listeneable data emitter.

Example
const emitter = new Emitter();
const unsubscribe = emitter.addListener(console.log);
emitter.emit('Hello World!'); // Console output: Hello World!
unsubscribe(); // Disconnects the listener from the emitter.
emitter.emit('Are you listening?'); // Console outputs nothing.

Fields​

  • .hasListeners — boolean — true if any listener is connected to the emitter; false otherwise.
  • .listeners — Array<Listener> — Array of listeners connected to the emitter. Although accessible for direct manipulations, addListener() and removeListener() methods should be preferred to add/remove listeners in most cases.

Methods​

constructor()​

const emitter = new Emitter<T extends unknown[] = unknown[]>();

Creates a new emitter with no listeners connected.

TypeScript: The optional generic parameter T specifies the exact set of arguments expected by emit() method of created emitter, and thus the signature and arguments received by connected listeners. It defaults to unknown[] — unknown set of arguments.

addListener()​

emitter.addListener(listener: Listener): function;

Connects given listener to the emitter, or does nothing if it is already connected. Each connected listener will be called once on each subsequent emit() call with the arguments passed into emit().

This method returns a function which can be triggered with no arguments to unsubscribe listener from the emitter. It is just an auxiliary wrapper around removeListener() method, which can be used alternatively.

emit()​

emitter.emit(...args: T);

Calls every connected listener once with the given arguments.

TypeScript: The argument types are specified by the generic parameter given to the constructor(), which defaults to unknown[].

removeAllListeners()​

emitter.removeAllListeners()

Diconnects all listeners from the emitter.

removeListener()​

emitter.removeListener(listener: Listener);

Disconnects given listener from the emitter, or does nothing if it is not connected to it.

Listener​

import type {Listener} from '@dr.pogodin/react-utils'; // or from '@dr.pogodin/js-utils'

type Listener<T extends unknown[] = unknown[]> = (...args: T) => void;

The Listener type specifies the valid signature of listener functions that can be attached to an instance of Emitter class. It accepts one optional generic parameter, that specifies valid arguments accepted by the listener. That parameter defaults to unknown[]