EventEmitter.js

module.exports = EventEmitter;

/**
 * Base class for objects that dispatches events.
 * @class EventEmitter
 * @constructor
 * @example
 *     var emitter = new EventEmitter();
 *     emitter.on('myEvent', function(evt){
 *         console.log(evt.message);
 *     });
 *     emitter.emit({
 *         type: 'myEvent',
 *         message: 'Hello world!'
 *     });
 */
function EventEmitter() {
}

EventEmitter.prototype = {
    constructor: EventEmitter,

    /**
     * Add an event listener
     * @method on
     * @param  {String} type
     * @param  {Function} listener
     * @return {EventEmitter} The self object, for chainability.
     * @example
     *     emitter.on('myEvent', function(evt){
     *         console.log('myEvt was triggered!');
     *     });
     */
    on: function ( type, listener, context ) {
        listener.context = context || this;
        if ( this._listeners === undefined ){
            this._listeners = {};
        }
        var listeners = this._listeners;
        if ( listeners[ type ] === undefined ) {
            listeners[ type ] = [];
        }
        if ( listeners[ type ].indexOf( listener ) === - 1 ) {
            listeners[ type ].push( listener );
        }
        return this;
    },

    /**
     * Remove an event listener
     * @method off
     * @param  {String} type
     * @param  {Function} listener
     * @return {EventEmitter} The self object, for chainability.
     * @example
     *     emitter.on('myEvent', handler); // Add handler
     *     emitter.off('myEvent', handler); // Remove handler
     */
    off: function ( type, listener ) {
        var listeners = this._listeners;
        if(!listeners || !listeners[type]){
            return this;
        }
        var index = listeners[ type ].indexOf( listener );
        if ( index !== - 1 ) {
            listeners[ type ].splice( index, 1 );
        }
        return this;
    },

    /**
     * Check if an event listener is added
     * @method has
     * @param  {String} type
     * @param  {Function} listener
     * @return {Boolean}
     */
    has: function ( type, listener ) {
        if ( this._listeners === undefined ){
            return false;
        }
        var listeners = this._listeners;
        if(listener){
            if ( listeners[ type ] !== undefined && listeners[ type ].indexOf( listener ) !== - 1 ) {
                return true;
            }
        } else {
            if ( listeners[ type ] !== undefined ) {
                return true;
            }
        }

        return false;
    },

    /**
     * Emit an event.
     * @method emit
     * @param  {Object} event
     * @param  {String} event.type
     * @return {EventEmitter} The self object, for chainability.
     * @example
     *     emitter.emit({
     *         type: 'myEvent',
     *         customData: 123
     *     });
     */
    emit: function ( event ) {
        if ( this._listeners === undefined ){
            return this;
        }
        var listeners = this._listeners;
        var listenerArray = listeners[ event.type ];
        if ( listenerArray !== undefined ) {
            event.target = this;

            // Need to copy the listener array, in case some listener was added/removed inside a listener
            var tmpArray = [];
            for (var i = 0, l = listenerArray.length; i < l; i++) {
                tmpArray[i] = listenerArray[i];
            }
            for (var i = 0, l = tmpArray.length; i < l; i++) {
                var listener = tmpArray[ i ];
                listener.call( listener.context, event );
            }
        }
        return this;
    }
};