封装函数--->切换class

        var obj={};
        obj.className=‘a b c d active‘;
        function toggle(obj,className) {
            var str=obj.className;
            var arr=str.split(" ");
            var onOff=true;
            for (var i = 0; i < arr.length; i++) {
                if(arr[i]===className){
                    onOff=false;
                    arr.splice(i,1);
                    i--;
                }
            }
            if (onOff) {
                arr.push(className);
            }
            obj.className=arr.join(" ");
            return obj.className;
        }


        function addClass(obj,className) {
            var str=obj.className;
            var arr=str.split(" ");
            for (var i = 0; i < arr.length; i++) {
                if(arr[i]===className){
                    return obj.className;
                }
            }
            arr.push(className);
            obj.className=arr.join(" ");
            return obj.className;
        }

        function removeClass(obj,className) {
            var str=obj.className;
            var arr=str.split(" ");
            for (var i = 0; i < arr.length; i++) {
                if(arr[i]===className){
                    arr.splice(i,1);
                    i--;
                }
            }
            obj.className=arr.join(" ");
            return obj.className;
        }