js封装方法

function getByClass(parent, tagname, classname) { /
        var aEls = parent.getElementsByTagName(tagname);
        var arr = [];
        var re = new RegExp('(^|\\s)' + classname + '(\\s|$)');
        for (var i = 0; i < aEls.length; i++) {
            if (re.test(aEls[i].className)) {
                arr.push(aEls[i]);
            }
        }
        return arr;
    }
    
    function addClass(obj, sClass) {
        var aClass = obj.className.split(' ');
        if (!obj.className) {
            obj.className = sClass;
            return;
        }
        for (var i = 0; i < aClass.length; i++) {
            if (aClass[i] === sClass) return;
        }
        obj.className += ' ' + sClass;
    }
    
    
    function removeClass(obj, sClass) {
        var aClass = obj.className.split(' ');
        if (!obj.className) return;
        for (var i = 0; i < aClass.length; i++) {
            if (aClass[i] === sClass) {
                aClass.splice(i, 1);
                obj.className = aClass.join(' ');
                break;
            }
        }
    }