获取file的路径

    function getObjectURL(file) {
      var url = null;
      if (window.createObjectURL != undefined) { // basic
        url = window.createObjectURL(file);
      } else if (window.URL != undefined) { // mozilla(firefox)
        url = window.URL.createObjectURL(file);
      } else if (window.webkitURL != undefined) { // webkit or chrome
        url = window.webkitURL.createObjectURL(file);
      }
      return url;
    }