JavaScript实现网页头部进度条刷新

<div id="barbg">   <div id="bar">   </div>  </div>

 <style>   *{margin:0;padding:0;}   #barbg{height:5px; background:rgb(149,143,143)}   #barbg div{width:0; height:5px; position:relative; background:rgb(230,10,10);}  </style>

 <script>   document.onreadystatechange = function(){    var bar = document.getElementById('bar');    var barbg = bar.parentNode;    var wd = document.body.scrollWidth || document.documentElement.scrollWidth;    var t = 10;    var d = 0;    var i = 0;    var timer = setInterval(goto,10);    function goto(){     d = d + t ;     bar.style.width = d + 'px';     if(d >= wd){      clearInterval(timer);      bar.style.background = 'rgba(230,10,10,0)';      none();     }    }    function none(){     var a = 10 - i;     i++;     if(a != 0 && a != 10){a = a * 0.1}     if(a === 10){a = 1}     if(a === 0){a = 0}     barbg.style.background = 'rgba(230,10,10,' + a + ')';     if(a === 0){barbg.style.display = 'none'}     if(a != 0){setTimeout(none,50);}    }   }  </script>