js判断登陆用户名及密码是否为空的简单实例

<script type="text/javascript">// 验证输入不为空的脚本代码function checkForm(form) {if(form.username.value == "") {alert("用户名不能为空!");form.username.focus();return false;}if(form.password.value == "") {alert("密码不能为空!");form.password.focus();return false;}return true;}</script>

<form action="#" method="post" onsubmit="return checkForm(this);">