javascript - 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);
    }
}