ajax等待效果

后台处理参数，生成结果数据：
data['plan_list'] = plans//data是字典
req.send(json.dumps(data).encode('utf-8'))//转成json数据
前台传送参数，接收结果
$.ajax({
	type:'post',url:"/myTrac/projectmanage/project/plan_project",data:{
		"new_plan_flag":'1',"plan_name":$('#plan_name_new').val(),"project_name":project_name,"stage_list":stage_list.join('[flag]'),__FORM_TOKEN:$('#trac_form_token').val()
	},async:true,//false无效果
	beforeSend: function(){
	var height = document.body.scrollWidth + "px";//滚动位置可能大于屏幕高度
	$('#bg').css("display","block").css("height",height).css("text-align","center").html('<img style="padding-top:300px;" 	src="/myTrac/chrome/projectmanage/images/wait.gif" />');
	},complete:function(data) {$('#bg').css("display","none");},//#bg是遮蔽层div
	success:function(data){
	data = eval("("+data+")");//解析json数据
		if(data.status = "Success"){
			alert("已保存")
		}else{
			alert('Create Fail,Please Check !')
		}
	}
});