js中字节单位自动转化，B，KB，MB，GB

function change(limit: number){
  var size = "";
  if(limit < 0.1 * 1024){                            //小于0.1KB，则转化成B
          size = limit.toFixed(2) + "B"
      }else if(limit < 0.1 * 1024 * 1024){            //小于0.1MB，则转化成KB
          size = (limit/1024).toFixed(2) + "KB"
      }else if(limit < 0.1 * 1024 * 1024 * 1024){        //小于0.1GB，则转化成MB
          size = (limit/(1024 * 1024)).toFixed(2) + "MB"
      }else{                                            //其他转化成GB
          size = (limit/(1024 * 1024 * 1024)).toFixed(2) + "GB"
      }
  
      var sizeStr = size + "";                        //转成字符串
      var index = sizeStr.indexOf(".");                    //获取小数点处的索引
      var dou = sizeStr.substr(index + 1 ,2)            //获取小数点后两位的值
      if(dou == "00"){                                //判断后两位是否为00，如果是则删除00               
          return sizeStr.substring(0, index) + sizeStr.substr(index + 3, 2)
      }
      return size;
  }