                        课程
                    
                        /前端开发
                        
                            /JavaScript
                        
                        /JS动画效果

不理解为什么一直提示联系.html:23 Uncaught TypeError: Cannot set property 'onmouseover' of nul ，检查了好多遍，不懂问题出在那块儿，哪位大神帮忙看下，谢谢l

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>
dbhs
   </title>
<style type="text/css">
div{
   width:200px;
   height:100px;
   background-color:yellow;
   border:2px solid #000;
   opacity: 0.3;
   filter:alpha(opacity:30);
}
</style>

<script type="text/javascript">

window.onload=function(){
   var odiv =document.getElementById("div");
odiv.onmouseover=function(){
    startMove(odiv,'width',400);
}
}

function startMove(obj,attr,iTarget,fn){
clearInterval(obj.timer);
obj.timer=setInterval(function(){
    var icur=null;
    if(attr=='opacity'){
      icur=Math.round(parseFloat(getStyle(obj,attr))*100);
    }else{
      icur=parseInt(getStyle(obj,attr));
    }
    var speed=(iTarget-icur)/10;
    speed=speed>0?Math.ceil(speed):Math.floor(speed);
    if(icur==iTarget){
      clearInterval(obj.timer);
      if(fn){
      fn();
    }
    }else{
      if(attr=='opacity'){
        obj.style.filter='alpha(opacity:'+(icur+speed)+')';
        obj.style.opacity=(icur+speed)/100;
      }else{
        obj.style[attr]=icur+speed+'px';
      }
    }

},30)
}

function getStyle(obj,attr){
        if(obj.currentStyle){
            return obj.currentStyle[attr];
        }else{
            return getComputedStyle(obj,false)[attr];
        }
    }
</script>
</script>
</head>
<body>
<div id="div1">

</div>
</body>
</html>