javascript中实现Timer.wait()功能

<script language="javascript">
	function f1(){   
		alert(1);   
		setTimeout(f2,1000);   
		function f2(){   
			alert(2);   
			setTimeout(f3,1000);   
			function f3(){   
				alert(3);   
			}   
		}   
	}   
	f1();   
</script>