Cross-browser function for adding an event listener

Here is a function that should work in virtually every browser, even really old ones. Of course, it is only useful, if you don’t use jQuery. Because, if you do, a far better way is to just call .on() or .bind() or .delegate() or .live() or whatever you want, and let jQuery do all the dirty work.

Function code:

[code language=”javascript”]
/**
* Adds event handler; works for all browsers, including old IE versions.
*
* @param event Event name (string) to attach.
* @param thefunction Function executed upon attached event fire (callback).
*/
function addListener(event, thefunction)
{
if(window.addEventListener)
{
//All browsers, except IE before version 9.
window.addEventListener(event, thefunction, false);
}
else if(window.attachEvent)
{
//IE before version 9.
event = (event == ‘DOMContentLoaded’) ? ‘onreadystatechange’ : "on" + event;
window.attachEvent(event, thefunction);
}
else
{
/**
* Code for really old ones — like NS4 or IE5Mac, which
* neither support attachEvent nor addEventListener
*
* This code is copyright 2003 by Gavin Kistner, !@phrogz.net
* It is covered under the license viewable at http://phrogz.net/JS/_ReuseLicense.txt
*
* More info: http://phrogz.net/JS/AttachEvent_js.txt
*/
if(!window.myEvents) window.myEvents = {};
if(!window.myEvents[event]) window.myEvents[event] = [];

var events = window.myEvents[event];
events[events.length] = thefunction;

window[‘on’ + event] = function()
{
if(!window || !window.myEvents || !window.myEvents[event]) return;

var events = window.myEvents[event];

for(var i = 0, len = events.length; i<len; i++) events[i]();
};
}
}
[/code]

Because I don’t have access to those “really old ones”, I cannot test and guarantee, that it will work there. Example used here comes from 2003, so it is itself “really old one”! :]