event-emitter-module

event-emitter-module

A simple Javascript event emitter

Installation

npm install event-emitter-module

Usage

Since the testing is not functional, it can be partially tested with the following. 
First instantiate a new Event Emitter from the class:
  const emitTest = new EventEmitter();

Methods

addListener(eventName, callbackFn){}
	-Adds a listener to an events object with the eventName as the key and callbackFn as the value

removeListener(eventName, callbackFn){}
	-Removes a listener to an events object based on the eventName and callbackFn passed in

removeAllListeners(){}
	-Remove all listeners from the events object (Should be able to pass in a specific eventName to target a specific listener)

once(eventName, callbackFn){}
	-Adds a listener that can be used up to one time and then removes that listener

emit(eventName, ...args){}
	-Emits the event and passes any arguments to the listeners that are looking for that event

Tests

The following are examples with expected output:
emitTest.addListener('change', (a, b) => {
  console.log(a, b);
});
emitTest.emit('change', 'a', 'b');
//expected output is: a b  

let m = 0;
emitTest.addListener('event', () => {
    console.log(++m);
});
emitTest.emit('event');
emitTest.emit('event');
//expected output is: 0
                      1
                      2

let n = 0;
emitTest.once('changeOnce', () => {
    console.log(++n);
});
emitTest.emit('changeOnce');
emitTest.emit('changeOnce');
//expected output is: 0
                      1                       

const callbackA = () => {
    console.log('A');
  emitTest.removeListener('newEvent', callbackB);
}
const callbackB = () => {
    console.log('B');
};

emitTest.addListener('newEvent', callbackA);
emitTest.addListener('newEvent', callbackB);
emitTest.emit('newEvent');
emitTest.emit('newEvent');
//expected output is: A
                      B
                      A

emitTest.emit('event');
 //since earlier 'event' was called expected output is: 3

emitTest.removeAllListeners('event');
emitTest.emit('event');
 //expected output is nothing since the listener was removed