js 多张图片加载 环形进度条

css 部分使用 svg 绘制环形

 svg{width:100px; height: 100px; margin:15% auto 25%; box-sizing:border-box; display: block;}
 svg circle{fill:none;cx:;cy:;}
  /* svg text{x:40;y:55;} 不起作用  原因不知*/
 svg #txt{ x:;y:55%;fill:red;}
 svg #backdrop{stroke-linecap:round;stroke:#333; stroke-width:2px;r:;}
 svg #progress{stroke:#690; stroke-dasharray:0 1000;stroke-width:3px;r:;}

此处的 js 放在 body 标签中

 var mulitImg = [
           'http://www.cctv.com/img/2.png',
           'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1520235078852&di=a57664a8e118c403bf2d378757e40b08&imgtype=0&src=http%3A%2F%2Fs9.knowsky.com%2Fbizhi%2Fl%2F100001-105083%2F2009530184324945217430590.jpg',
           'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1520235078852&di=0a127ba0bf50857c86bd886ef355d2c9&imgtype=0&src=http%3A%2F%2Fpic1.win4000.com%2Fwallpaper%2F4%2F593a3dba085e1.jpg',
           'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1520235078851&di=f1dacfe012d7e71c7469a4b0b4df2708&imgtype=0&src=http%3A%2F%2Fpic1.win4000.com%2Fwallpaper%2Fe%2F5902ad376edd5.jpg',
           'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1520235078851&di=b6ab0dcfbe939057988cabb0bd0f3899&imgtype=0&src=http%3A%2F%2Fpic1.win4000.com%2Fwallpaper%2F1%2F535a1f52d5f8c.jpg',
           'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1520235078850&di=4f0693db95d8e117035f77d7a1d5e493&imgtype=0&src=http%3A%2F%2Fpic1.win4000.com%2Fwallpaper%2Ff%2F594336ec75b26.jpg'

        ];
   // 调用函数， 传入图片数组
   load_img(mulitImg);
   function load_img(mulitImg)
   {
      var svg=document.createElementNS('http://www.w3.org/2000/svg','svg');
        document.body.appendChild(svg);
       var svg_html='<circle id="backdrop" /><text x="35" y="55%" fill="red" id="txt">0%</text><circle id="progress"  />';
         svg.innerHTML=svg_html;

      var idtxt=document.getElementById('txt');
      var progrees=document.getElementById('progress');
      var pro_v=parseInt(css(progrees,'stroke-dashoffset'));
      var r=parseInt(css(progrees,'r'));     // 半径
      var arcLength=Math.floor(2*Math.PI*r); // 周长

      var taget=100;
      var img = [],
           flag = 0; 

        var imgTotal = mulitImg.length;
             //添加过渡效果
            progrees.style.transitionDuration=arcLength/imgTotal/100+'s';
            idtxt.style.transitionDelay=arcLength/imgTotal/100/2+'s';

        for(var i = 0 ; i < imgTotal ; i++){
           img[i] = new Image();
           img[i].index=i;
           img[i].src = mulitImg[i]
           // 图片加载完成
           img[i].onload = function(){

              //第i张图片加载完成
              flag++;
              idtxt.textContent=(flag/imgTotal).toFixed(2) *100+'%';
              progrees.style.strokeDasharray=arcLength*(flag/imgTotal)+' 1000';// 第二个值必须大于周长

              if( flag == imgTotal ){
                 //全部加载完成
              }
           };
           // 图片加载失败----继续执行，可以选择用另一张图片替换
           img[i].onerror = function(){
              //第i张图片加载失败

              flag++;  // 继续执行
              // console.log(this.index+':'+this.src)
             idtxt.textContent=(flag/imgTotal).toFixed(2) *100+'%';
              progrees.style.strokeDasharray=arcLength*(flag/imgTotal)+' 1000';// 第二个值必须大于周长
              if( flag == imgTotal ){
                 //全部加载完成
              }
           };
        }

       // 获取css 样式
       function css(t, n) {
           return t.currentStyle ? t.currentStyle[n] : getComputedStyle(t, !1)[n]
         }
   }