解决 IE 不支持 document.getElementsByClassName() 的方法

//create method getElementsByClassName for document
    if(!document.getElementsByClassName){
        document.getElementsByClassName = function(className, element){
            var children = (element || document).getElementsByTagName(‘*‘);
            var elements = new Array();
            for (var i=0; i<children.length; i++){
                var child = children[i];
                var classNames = child.className.split(‘ ‘);
                for (var j=0; j<classNames.length; j++){
                    if (classNames[j] == className){ 
                        elements.push(child);
                        break;
                    }
                }
            } 
            return elements;
        };
    }