我是 JavaScript 新手，一直在这里搜索线程，但无法弄清楚为什么我的表单没有正确运行验证。我已尝试添加警报以查找问题，它似乎在第一个 IF 语句附近。有任何想法吗？谢谢！
<script type="text/javascript">
function dataCheck()
{
var firstName = document.getElementById("firstName").value;
var firstName = document.myForm.firstName.value;
var lastName = document.getElementById("lastName").value;
var facilitator = document.getElementById("facilitator").value;
//validate firstName field for minimum of 2 characters
if (firstName.length < 2){
alert("Please enter a first name with a minimum of 2 characters");
return false;
}
else {retvalue = true}
//validate lastName field for min length and numeric or alpha characters only
if (lastName.length < 2 || lastName.){
alert("Please enter a last name with a minimum of 2 characters");
return false;
}
if( /[^a-zA-Z0-9]/.test(lastName) ) {
alert("Last name must be alphanumeric.");
return false;
}
}
</script>
<form action="http://bucs601.com/submit.php" name="myForm" onsubmit="return dataCheck()" method="post">
First name: <input type="text" id="firstName" name="firstName"><br>
Last name: <input type="text" id="lastName" name="lastName"><br>
Email: <input type="text" id="email" name="email"><br>
Facilitator: <input type="text" id="facilitator" name="facilitator">
<input type="submit" id="submit" value="Submit">
</form>