关于“form控件的动态修改”和“弹出窗口的创建”（附源码）

<html>
<head>
<title>
CRM-system[index]
</title>
<script language="javascript" type="text/javascript">
<!--
var popWindow = window.createPopup();function validateField()
{
if (window.document.LoginActionForm.username.value == "")
    {
alert(window.document.LoginActionForm.username.name + " can't be empty!");
window.document.LoginActionForm.username.focus();
window.document.LoginActionForm.username.style.backgroundColor="red";
return false;
    }
else if (window.document.LoginActionForm.password.value == "")
{
alert(window.document.LoginActionForm.password.name + " can't be empty!");
window.document.LoginActionForm.password.focus();
return false;
}
else
return true;
}function showPopWindow()
{
var popBody = popWindow.document.body;
popBody.style.backgroundColor = "#ffff99";
popBody.style.border = "solid black 1px";
popBody.innerHTML = " Can't be empty!";
popWindow.show(event.clientX,event.clientY,120,25,document.body);
}
function closePopWindow()
{
popWindow.hide();
}
//-->
</script>
</head>
<body >
<center>
<h1></h1>
<h1 color="blue">CRM SYSTEM</h1>
<p>
<form name="LoginActionForm" method="POST" action="/crm/loginAction.do" onsubmit="return validateField()">
Please input username:
<input type="text" name="username" maxlength="8" size="8" value="robert" 
onmouseover="showPopWindow();" onmouseout="closePopWindow();">
<br>
Please input password:
<input type="password" name="password" maxlength="8" size="8" value="robert" onmouseover="showPopWindow();" onmouseout="closePopWindow();">
<p>
<input type="submit" name="submit" value="提 交"> <input type="reset" value="Reset">
</form>
&#x00A9; DreamScope Information Technology co. ltd.
</center>
</body>
</html>