javascript+css实现进度条效果

<div class="progress_area">
 <span id="progress" class="progress_bac"></span>
</div>
<input type="button" class="progress-inp" value="100%" οnclick="progress(100);"/>
<input type="button" class="progress-inp" value="86%" οnclick="progress(86);" />
<input type="button" class="progress-inp" value="20%" οnclick="progress(20);"/>

.progress_area{
 width: 255px;
 height: 13px;
 border: 1px solid #c;
 border-radius: 15px;
 margin-bottom: 30px;
}
.progress-inp{
 width: 60px;
 height: 28px;
 border: 1px solid #c;
 background: #62c7ef;
 border-radius: 8px;
 color: white;
 cursor: pointer;
 outline:none;
}
.progress_bac{
 display: block;
 height: 100%;
 width: 50%;
 background: #83a4f1;
 border-radius: 10px;
}

.progress_bac{
 display: block;
 height: 100%;
 width: 50%;
 background: #83a4f1;
 border-radius: 10px;
 -moz-box-shadow:0px 0px 7px 0px #4486ca;
 -webkit-box-shadow:0px 0px 7px 0px #4486ca;
 box-shadow:0px 0px 7px 0px #4486ca;
}

.progress_bac{
 display: block;
 height: 100%;
 width: 50%;
 background: #83a4f1;
 border-radius: 10px;
 -moz-box-shadow:0px 0px 7px 0px #4486ca;
 -webkit-box-shadow:0px 0px 7px 0px #4486ca;
 box-shadow:0px 0px 7px 0px #4486ca;
 -moz-transition: width 0.5s;
 -webkit-transition: width 0.5s;
 transition: width 0.5s;
}

function progress(value){
 if ( value ){ 
  var num = "";
  var loader_progress = setInterval(function(){
   num++;
   document.getElementById("progress").style.width = num+"%";
   if ( num == value ){
    clearInterval(loader_progress);
   }
  },10);
 }
};