实现逻辑：
1. 创建两个互调用函数 setTitle1和setTitle2
2. 定时调用机制
3. 窗体获取焦点和失去焦点存状态
4. 来消息了存状态（在本例中，模拟每3秒来1个消息）
5. 在setTitle1中判断状态

完整代码：

<script src="jquery-1.10.2.js" ></script>
	<div class="pnl"></div>


<script>	
		var newMsg = false;
        var window_focused = true;
		
		setInterval(function(){		
			$(".pnl").append("<div>new msg</div>");
			newMsg = true;
		}, 3000);
		
		
		function setTitle1(){
			if(newMsg === true && window_focused === false){
				document.title = "New Msg";
				setTimeout(setTitle2,100);
			}
		}
		
		function setTitle2(){
				document.title = "";
				setTimeout(setTitle1,100);
		}
		
		setInterval(setTitle1, 1000);
		
		$(window).focus(function (e) {
            window_focused = true;
        });


        $(window).blur(function (e) {
            window_focused = false;
        });
		
		</script>