signal-js

A small (2.4KB minified, 1.07KB gzipped) and fast event system with 0 dependencies. Written in es2020 and built for performance. Great as a pubsub or to add event emitters to your code.

Installation

npm install signal-js

How to use

Add a function to signal using on and trigger the function using emit

import signal from 'signal-js';

signal.on('basic', arg => console.log(arg);

signal.emit('basic', 1);
// > 1

Add multiple functions to the same event name

import signal from 'signal-js';

signal.on('multiple', () => console.log(1));
signal.on('multiple', () => console.log(2));
signal.on('multiple', () => console.log(3));

signal.trigger('multiple');
// > 1
// > 2
// > 3

Pass as many parameters as you need

import signal from 'signal-js';

signal.on('params', (one, two, three) => console.log(one, two, three));

signal.emit('params', 1, 2, 3);
// > 1 2 3

Remove events using off

import signal from 'signal-js';

signal.on('test', () => console.log('hi'))
  .off('test') // removes all `test` events
  .emit('test'); // nothing happens

once can also be used

import signal from 'signal-js';

let idx = 0;
signal.once('tick', () => idx++);

signal.emit('tick')
// idx = 1

signal.emit('tick');
// idx = 1

The exposed signal is a singleton, but other instances can also be created:

import signal from 'signal-js';

signal.on('foo', () => console.log('global'));

const local = signal();
local.on('foo', () => console.log('local'));

const local2 = local();
local2.on('foo', () => console.log('local2'));

signal.emit('foo');
// > "global"

local.emit('foo');
// > "local"

local2.emit('foo');
// > "local2"

API

.on(eventName, listener)

• eventName string The name of the event
• listener Function The event handler
• Returns: signal

Alias: addListener, subscribe, bind

.off(eventName, listener)

• eventName string The name of the event
• listener Function (optional) The event handler
• Returns: signal

If listener is passed, the specific listener will be unbound, otherwise all listeners under eventName will be unbound.

Alias: removeListener, unsubscribe, unbind

.emit(eventName, [...parameters])

• eventName string The name of the event
• parameters any (optional) The arguments passed to the listener
• Returns: signal

Alias: dispatch, trigger

.once(eventName, listener)

• eventName string The name of the event
• parameters any The event handler
• Returns: signal

Adds a one-time listener that will remove itself after being invoked.

.listeners(eventName)

• eventName string The name of the event
• Returns: Array

Retrieves registered listeners under the eventName. If no eventName is passed, returns all listeners.

.keys()

• Returns: Array

Retrieves all eventNames.

.size(eventName)

• eventName string The name of the event
• Returns: Number

Returns the quantity of listeners at the given eventName. If no eventName is passed, returns the quantity of all listeners.

.clear(eventName)

• Returns: signal Forcefully clears all listeners and eventNames from the signal at the eventName. Clears all listeners if no eventName is passed.