Further Explorations - HTML5 Canvas - page 913

addEventListener()

Allows us to add a listener (subscriber) for a particular event

dispatch()

Allows us to send events to listeners

removeEventListener() removeEventListener()

Allows us to remove a listener when it is no longer needed

By defining all the preceding methods as properties of the EventDispatcher prototype
( EventDispatcher.prototype.addEventListener() ),anotherclasswillbeabletousethis
class as a base class and inherit all of them.

//Adapted from code Copyright (c) 2010 Nicholas C. Zakas. All rights reserved.
//MIT License

function function EventDispatcher (){

this

this . _listeners = {};

}
EventDispatcher . prototype . addEventListener = function

function ( type , listener ){

iif ( typeof typeof this this . _listeners [ type ] == "undefined" ){

this this . _listeners [ type ] = [];

}
this

this . _listeners [ type ]. push ( listener );

}
EventDispatcher . prototype . dispatch = function function ( event ){

iif ( typeof typeof event == "string" ){

event = { type : event };

}
iif ( ! event . target ){
event . target = this

this ;

}
iif ( ! event . type ){ //false
throw

throw new new Error ( "Event object missing 'type' property." );

}
iif ( this

this . _listeners [ event . type ] instanceof instanceof Array ){

var var listeners = this this . _listeners [ event . type ];

for for ( var var i = 0 , len = listeners . length ; i < len ; i ++ ){

listeners [ i ]. call ( this

this , event );

}

}

}