How to solve .length issue after getElementsByClassName hack in ie?

Question

JavaScript

There is a parallax.js library which has getElementsByClassName. To work in IE7> registered:

function getElementsByClassName(node, classname) {
  var a = [];
  var re = new RegExp('(^| )'+classname+'( |$)');
  var els = node.getElementsByTagName("*");
  for(var i=0,j=els.length; i<j; i++)
    if(re.test(els[i].className))a.push(els[i]);
  return a;
}
var parallaxLayer = getElementsByClassName(document.body,'layer');

But now the error in all browsers is: " Cannot read property 'length' of undefined " (chrome, opera), " Unable to get property 'length' of undefined or null reference " (IE), " this.layers is undefined " (FF ).
Is it possible to solve this problem?
Here is a small code example (comments where the getElementsByClassName method is replaced and where it throws an error with length)

Answer 1

I wonder why you need support for IE 7?