<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
function formCheck(){//表单验证
var userForm=document.forms.userForm
if(userForm.username.value==null||userForm.username.value.length<=0){
alert("用户名不能为空")
return false
}else if(userForm.username.value.length<6||userForm.username.value.length>20){
alert("用户名必须为6-20位")
return false
}else if(userForm.password.value==null||userForm.password.value.length<=0){
alert("密码不能为空")
return false
}else if(userForm.password.value.length<6||userForm.password.value.length>20){
alert("密码必须为6-20位")
return false
}else{
userForm.submit()
}
}
</script>
</head>
<body>
<form action="" name="userForm">
userName:<input type="text" name="username"><br>
password:<input type="password" name="password"><br>
<input type="button" value="提交" onclick=" formCheck()">
</form>
</body>
</html>
可以在submit按钮上添加onclick事件。通过创建function函数进行验证，全部通过后执行form.submit()，错误则利用alert或者innerHTML显示错误信息。
