这里的that.Ul.style.left值 怎么写才能保存住上次的值

// css 部分

   *{
        margin: 0;
        padding: 0;
    }
    .scroll{
        overflow: hidden;
        clear: both;
        width: 1200px;
        margin: 0 auto;
        position: relative;
    }
    .scroll li{
        width: 280px;
        float: left;
        list-style: none;
    }
    .scroll .pre{
        width:30px;
        height: 240px;
        line-height: 240px;
        background: #ccc;
        float: left;
        text-align: center;
        font-size: 18px;
        font-weight: bold;
        margin-right: 10px;
        position: absolute;

    }
    .scroll .next{
        right: 0;
    }
    .scroll .pre a{
        display: block;
        text-decoration: none;
    }

    .scroll ul{
        width: 1000000px;
        overflow: hidden;
        float: left;
        left: 0;
        position: absolute;
        transition: all 0.5s ease 0s;
    }

    .scroll .active,.scroll .pre a:hover{
        background: #05c0e2;
        color:#fff;
    }
    .last{
        background: #ccc;
    }
    #jsulbox{
        width:1100px;
        overflow: hidden;
        height: 240px;
        left:40px;
        overflow: hidden;
        position: relative;
        float: left;
    }
    .prenext{
        width: 100%;
    }

//HTML 部分

      
<
      

         

             

             

             

             

             

             

             

             

         
     

    
>

// javascript 部分