Adding custom class to an element

add_class

var add_class = function(element, classname) {
    var class_name = element.className;
    //test for existance
    if( class_name.indexOf( classname ) !== -1 ) {
        return;
    }
    //add a space if the element already has class
    if( class_name !== '' ) {
        classname = ' '+classname;
    }
    element.className = class_name+classname;
}