eventemitter16 v0.1.0

eventemitter16

A custom event emitter to replace Node’s built in eventemitter

• It is small but very powerful
• It is built with classes
• It doesn't use any dependencies
• It has better errors thrown in case of a user mistake
• It is easy to implement
• It executes all methods synchronously and in order of addition emitter.prependListener() and emitter.prependOnceListener() are not included
• It has an additional Util class you can access in eventemitter16 instances
• It is easy to extend

Examples

• Simple emitter logging "Hello world!"

const EventEmitter = require('eventemitter16'); // Import the module
const emitter = new EventEmitter; // Create an instance of it

emitter.on('hello', function hello() { // Listen to the event
  console.log("Hello world!");
});

emitter.emit('hello'); // Invokes all listeners for 'hello'

• Simple emitter executing functions and giving them arguments

const EventEmitter = require('eventemitter16'); // Import the module
const emitter = new EventEmitter; // Create an instance of it

emitter.on('exec', function exec(hello, world) { // Listen to the event
  console.log(hello + ' ' + world);
  emitter.emit('qwerty', hello, world); // Invokes all listeners for 'qwerty'
});

emitter.on('qwerty', function qwerty(...args) { // Listen to the event
  console.log(args.join(' ');
});

emitter.emit('exec', 'Hello', 'world!'); // Invokes all listeners for 'exec'

• Simple testing application logging the eventnames and listeners

const EventEmitter = require('eventemitter16'); // Import the module
const emitter = new EventEmitter; // Create an instance of it

emitter.on('qwerty', () => {}) // Chaining events is also possible!
  .on('message', () => {})
  .on('message', () => {}); // Won't be logged twice

console.log(emitter.eventNames()); // [ 'qwerty', 'message' ]

const listeners = emitter.listeners(); // 3 empty methods

console.log(listeners.map(fn => fn.toSource()));

• Simple emitter listening to events only once

const EventEmitter = require('eventemitter16'); // Import the module
const emitter = new EventEmitter; // Create an instance of it

emitter.on('message', msg => { // Listen to the event
  console.log(msg);
}).once('message', msg => { // Will be removed and then invoked
  msg = msg.split('').reverse().join('');
  console.log(msg);
});

emitter.emit('message', 'drooM'); // Invokes all listeners for 'message'
emitter.emit('message', 'Hello world!'); // Won't invoke the second listener since it got removed

• Simple emitter listening to 'newListener' Fired when a new listener is added

const EventEmitter = require('eventemitter16'); // Import the module
const emitter = new EventEmitter; // Create an instance of it

emitter.on('newListener', function newListener(event, listener) { // This will emit itself
  console.log(`[${event}] Amount of parameters: ${listener.length}`);
});

emitter.on('qwerty', function qwerty(alphabet) { // Emits 'newListener'
  console.log(alphabet);
});

Doing this, however, has 1 flaw. It will emit itself. But thankfully, there is an easy workaround for this. Add this to the first line of the callback function:

if (event === 'newListener') return;

• Simple emitter removing listeners

const EventEmitter = require('eventemitter16'); // Import the module
const emitter = new EventEmitter; // Create an instance of it

var count = 0;

function listener() { // So you don't have to copy paste
  console.log('Hello world!');
  if (++count === 5) emitter.removeListener('listener', listener); // Easy and lightweight
}

emitter.on('listener', listener); // Easy and lightweight

while (emitter.listenerCount('listener')) { // While there are listeners for 'listener'
  emitter.emit('listener');
} // Doing like this prevents memory leaks