getElementsByClassName.js

var getElementsByClassName = function(name) {
    if(document.getElementsByClassName)
        return document.getElementsByClassName(name);
    
    else if(document.querySelectorAll)
        return document.querySelectorAll('.' + name);

    else {
        var list = document.getElementsByTagName('*'), i = list.length,
        array = name.split(/\s+/), result = [];

        while(i--) {
            if(list[i].className.search('\\b' + array + '\\b') != -1)
                result.push(list[i]);
        }
        return result;
    }
};