jQuery blockUI插件在ajax提交的时候的用处

$.ajax({
							type: "POST",
							 url: "GetFreeStand.do",
							 data:   "hid="+$("#hall").val()+"&pid="+$("#plan").val(),
							 dataType:'json',
							 async: false,
							 beforeSend:function(){
				 				$.blockUI({message:'获取大厅大厅的空闲摊位，请稍候...'});
				 			},
				 			complete: function() {
			                    $.unblockUI(); 
			                } ,
							 success: function(data){	
							 	$("#stand").empty();
							 	for(var i=0;i<data.rows.length;i++){
							 		var row = data.rows[i];						
									$("#stand")[0].options.add(new Option(row.name,row.id));
							 	}
							 } 
						});