//判断元素是否有class
function hasClass(ele, cls) {

        return ele.className.match(new RegExp('(\\s|^)'+cls+'(\\s|$)'));

    }
//元素增加class

    function addClass(ele, cls) {

        if (!hasClass(ele, cls)) ele.className += " "+cls;

    }
//元素移除class

    function removeClass(ele, cls) {

        if (hasClass(ele, cls)) {

            var reg = new RegExp('(\\s|^)'+cls+'(\\s|$)');

            ele.className = ele.className.replace(reg, ' ');

        }

    }

    /* className, rootId(限制范围id名), tagName(标签名称)*/

    function getElementsByClassName(cls, rid, tag) {

        root = rid && document.getElementById(rid) || document;

        if (root.getElementsByClassName) {

            return root.getElementsByClassName(cls);

        }

        tag = tag || '*';

        var elems = root.getElementsByTagName(tag);

        var ret = [];

        for (var i = 0, len = elems.length; i < len; i++) {

            var elem = elems[i];

            if ((' ' + elem.className + ' ').indexOf(' ' + cls + ' ') > -1) {

                ret.push(elem);

            }

        }

        return ret;

    }