three.js/src/core/EventDispatcher.js

/**
 * https://github.com/mrdoob/eventdispatcher.js/
 */

THREE.EventDispatcher = function () {

	var listeners = {};

	this.addEventListener = function ( type, listener ) {

		if ( listeners[ type ] === undefined ) {

			listeners[ type ] = [];

		}

		if ( listeners[ type ].indexOf( listener ) === - 1 ) {

			listeners[ type ].push( listener );

		}

	};

	this.removeEventListener = function ( type, listener ) {

		var index = listeners[ type ].indexOf( listener );

		if ( index !== - 1 ) {

			listeners[ type ].splice( index, 1 );

		}

	};

	this.dispatchEvent = function ( event ) {

		var listenerArray = listeners[ event.type ];

		if ( listenerArray !== undefined ) {

			event.target = this;

			for ( var i = 0, l = listenerArray.length; i < l; i ++ ) {

				listenerArray[ i ].call( this, event );

			}

		}

	};

};