js 失去焦点时关闭层实现代码

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml"> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" /> 
<title>失去焦点时关闭层练习</title> 
<style type="text/css"> 
#divUserName{ 
    width:200px; 
    height:30px; 
    border:1px solid black; 
    background:#cccccc; 
    font-size:12px; 
    margin-top:10px; 
} 
</style> 
<script language="javascript" type="text/javascript"> 
    window.onload = function(){ 
        document.getElementById("tbxUserName").focus(); 
        document.getElementById("tbxUserName").onblur = function(){ 
            document.getElementById("divUserName").style.display = 'none'; 
        } 
        document.getElementById("tbxUserName").onfocus = function(){ 
            document.getElementById("divUserName").style.display = ''; 
        } 
         
    } 
</script> 
</head>

<body> 
<input type="text" id="tbxUserName" />这是一个层 
</body> 
</html>

[Ctrl+A 全选注:如需引入外部Js需刷新才能执行]