code: function(callback) {
  			var self = this;
  			self.callback = callback;
  			self.mask.show();
  			document.body.classList.add($.className('poppicker-active-for-page'));
  			self.panel.classList.add($.className('active'));
  			//处理物理返回键
  			self.__back = $.back;
  			$.back = function() {
  				self.hide();
  			};
  		}
docs: 显示