javascript每日一练（十一）——多物体运动

一、多物体运动

　　需要注意：每个运动物体的定时器作为物体的属性独立出来互不影响，属性与运动对象绑定，不能公用；
例子1：
 <!doctype html>
 <html>
 <head>
 <meta charset="utf-8">
 <title>多物体运动</title>
 <style>
 div{ width:100px; height:100px; background:red; float:left; margin:10px; border:1px solid black; opacity:0.3; filter:alpha(opacity=30);}
 </style>
 <script>
 window.onload = function()
 {
     var aDiv = document.getElementsByTagName('div');

     aDiv[0].onmouseover = function()
     {
         startMove(this, 'width', 300);
     };
     aDiv[0].onmouseout = function()
     {
         startMove(this, 'width', 100);
     };

     aDiv[1].onmouseover = function()
     {
         startMove(this, 'height', 300);
     };
     aDiv[1].onmouseout = function()
     {
         startMove(this, 'height', 100);
     };

     aDiv[2].onmouseover = function()
     {
         startMove(this, 'opacity', 100);
     };
     aDiv[2].onmouseout = function()
     {
         startMove(this, 'opacity', 30);
     };

     aDiv[3].onmouseover = function()
     {
         startMove(this, 'borderWidth', 20);
     };
     aDiv[3].onmouseout = function()
     {
         startMove(this, 'borderWidth', 1);
     };
 };

 function getStyle(obj, attr)
 {
     if(obj.currentStyle){
         return obj.currentStyle[attr];
     }else{
         return getComputedStyle(obj, false)[attr];
     }
 }

 function startMove(obj, attr, iTarget)
 {
     clearInterval(obj.timer);

     obj.timer = setInterval(function(){
         var iCur = 0;

         if(attr == 'opacity'){
             iCur = parseInt(parseFloat(getStyle(obj, attr)) * 100);
         }else{
             iCur = parseInt(getStyle(obj, attr));
         }

         var iSpeed = (iTarget - iCur) / 8;
         iSpeed = iSpeed > 0 ? Math.ceil(iSpeed) : Math.floor(iSpeed);

         if(iCur == iTarget){
             clearInterval(obj.timer);
         }else{
             if(attr == 'opacity'){
                 obj.style.filter = 'alpha(opacity='+ (iCur+iSpeed) +')';
                 obj.style.opacity = (iCur+iSpeed)/100;
             }else{
                 obj.style[attr] = iCur + iSpeed + 'px';
             }
         }

     }, 30);
 }
 </script>
 </head>

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