this.fomatNum = function(num) {
      var str = num.toFixed(this.option.decimal);//精确到小数位数多少位
      var num1, x1, x2, reg;
      arr = str.split(".");
      x1 = arr[0];
      x2 = arr.length > 1 ? '.' + arr[1] : "";
      reg = /(\d+)(\d{3})/;
      if (this.option.isfomat) {
        while (reg.test(x1)) {
          x1 = x1.replace(reg, '$1' + "," + "$2");
        }
      }
      if (this.option.isfomat) {
        return this.option.prefix + x1 + x2;
      } else {
        return this.option.prefix + str;
      }
    }

var change = function() {
  var p = Math.min(1.0, (new Date().getTime() - that.startTime) / that.option.duration);//当前时间减去开始时间，然后除以总时间，Math.min,两个数取最小值。
  var nums = that.num * p;
  that.elm.innerHTML = that.fomatNum(that.num * p);
  if (p < 1.0) {//
     requestAnimationFrame(function() {
        change();
     });
   } else {
        cancelAnimationFrame(change);
       }
  }
  requestAnimationFrame(function() {
     change();
   });