转自：https://blog.csdn.net/qiu512300471/article/details/23259811
<script type="text/javascript">
function beforeSubmit(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;
}
if(form.password.value.length<6){
alert(‘密码至少为6位，请重新输入！‘);
form.password.focus();
return false;
}
if(form.password.value!=form.password2.value) {
alert(‘你两次输入的密码不一致，请重新输入！‘);
form.password2.focus();
return false;
}
return true;
}
</script>
<fieldset>
<legend>用户注册</legend>
<form method="post" name="form" action="user.do?method=register" onSubmit="return beforeSubmit(this);">
<table border="1" width="100%" cellspacing="0" cellpadding="0">
<tr><td><label>用户名：<input type="text" name="username" value=""></label></td></tr>
<tr><td><label>密 码：<input type="password" name="password" value=""></label></td></tr>
<tr><td><label>重复密码：<input type="password" name="password2" value=""></label></td></tr>
<tr><td><input value="注册" type="submit"> <input type="reset" value="重置"></td></tr>
</table>
</form>
</fieldset>
JS判断提交表单不能为空 等的验证
原文地址：https://www.cnblogs.com/sharpest/p/10160794.html