История изменений

if(!document.getElementsByClassName) {       
    document.getElementsByClassName = function (class_name) {
        var elements = document.body.getElementsByTagName("*"),
            length   = elements.length,
            out = [], i;
 
        for (i = 0; i < length; i += 1) {
            if (elements[i].className.indexOf(class_name) !== -1) {
                out.push(elements[i]);
            }        
        }         
        return out;
    };
}
for(elem in document.getElementsByClassName('elem')){
    if (!elem.hasOwnProperty(prop)) continue;

    if (elem.getAttribute('style'))
        elem.style.cssText = "styles";
    else 
        elem.setAttribute('style', "styles");
}

if(!document.getElementsByClassName) {       
    document.getElementsByClassName = function (class_name) {
        var elements = document.body.getElementsByTagName("*"),
            length   = elements.length,
            out = [], i;
 
        for (i = 0; i < length; i += 1) {
            if (elements[i].className.indexOf(class_name) !== -1) {
                out.push(elements[i]);
            }        
        }         
        return out;
    };
}
document.getElementsByClassName('elem').className = 'имя_класса'