老师要求做的《装小蜜》的项目，可是为什么我的start 是undefined?

Question

<div class="bottom clearfix" id="bottom">
                <div class="one" id="div1">
                    <img src="../images/smallpic.png">
                    <span class="span" id="sp1">
                        <strong class="s1">家装监理</strong>
                        <em class="s2">4大验收阶段 78项验收标准全程把关</em>
                    </span>
                </div>
                <div class="two" id="div2">
                    <img src="../images/smallpic.png">
                    <span class="span" id="sp2">
                        <strong class="s1">家装监理</strong>
                        <em class="s2">4大验收阶段 78项验收标准全程把关</em>
                    </span>
                </div>
<div>
    var sp1 = document.getElementById("sp1");
    var sp2 = document.getElementById("sp2");
    var div1 = document.getElementById("div1");
    var div2 = document.getElementById("div2");
    var bottom = document.getElementById("bottom");
    var divs = bottom.getElementsByTagName("div");
    var spans = bottom.getElementsByTagName("span");
    var speed =-10;
    var start =260;
    var timer ;
    var timerout;
for (var i = 0; i < divs.length; i++) {
        // divs[i].index = i;
        divs[i].onmouseover=function(num){
         return function(){
            if (timer) {
                clearInterval(timer);
                start=260;
                
            };
            timer = setInterval(function(){
            start +=speed;
            if (start<=0) {
                start=0;
                clearInterval(timer);
            };
            // console.log(this.index);
            spans[num].style.top = start+"px";
        },100)
        }}(i)
    
    };
    for (var i = 0; i < divs.length; i++) {
        divs.index = i;
        divs[i].onmouseout = function(){
            timerout = setInterval(function(){
                **start = parseInt(spans[this.index].style.top);**
                start -=speed;
                spans[this.index].style.top = start+"px";
            },100);
        }
    };
}

Answer 1

spans[this.index].style 中的这个 style 获取的是行内样式，你没有设置行内样式它就是undefined