Why am I getting TypeError: obj.addEventListener is not a function?

Question

Here's my code:

function addEvent( obj, type, fn ) {   if ( obj.attachEvent ) {     obj['e'+type+fn] = fn;     obj[type+fn] = function(){obj['e'+type+fn]( window.event );}     obj.attachEvent( 'on'+type, obj[type+fn] );   } else     obj.addEventListener(type, fn, false); }  function alertWinner(){     alert("You may be a winner!"); }  function showWinner (){     var aTag = document.getElementsByTagName("a");     addEvent(aTag, 'click', alertWinner); }  showWinner(); 

Basically, I'm working in the firebug console and trying to get an alert to pop up when any a tag is clicked.

I can't see the problem that results in this not working and giving me the error stated in my questions title (viewed in firebug). Anybody?

Answer 1

document.getElementsByTagName returns a NodeList of DOM elements. Each element has an addEventListener function, but the array doesn't have one.

Loop over it:

function showWinner (){     var aTags = document.getElementsByTagName("a");     for (var i=0;i<aTags.length;i++){         addEvent(aTags[i], 'click', alertWinner);     } }