<style>

   body{
    width:100%;
    height:100%;
    background: url();

}
</style>



<script>

setInterval(function()
{
//创建rain元素
var rain =document.createElement("div");

//初始化rain属性

rain.style.position = "fixed";
rain.style.height   = "150px";
rain.style.width    = "2px";
rain.style.background = "url(image/rain.png)";
rain.style.filter = "blur(1px)";
rain.style.top    = "0px";
rain.style.left   = Math.random()*1920+"px";           //随机化位置
rain.style.opacity= parseInt(Math.random()*10)/10+"";  //随机化透明度

//像body里添加子节点rain

document.body.appendchild(rain);

var timer = setInterval(  function()
 
 {
   var height = parseInt(rain.style.top);
   var k      =1;
   k++;
    
   rain.style.top = height+5*Math.pow(k,2)+"px";    //模拟重力加速度
   

   //当雨滴到达底部后消失并清除子节点rain

  if(rain.style.top>="900px")
   {
     clearInterval(timer);
     rain.parentNode.removeChile(rain);
  
    }
  

   },10)









},10)
