JS表单验证是不工作的html表单

我有一个简单的HTML表单。格式如下-

<table>
  <form method="post" action="insert.php"  name="idea_1" id="idea_1" onsubmit="return idea_1_check();" >    
    <input type="hidden" name="type" value="idea" />    
    <tr><td></td><td><br><h3 style="color:#990066; font-weight:bold;">First Member (Team Leader)</h3><br></td></tr> 
    <tr><td></td><td><input type="text" name="stu_name_1" value="" placeholder="Your Full Name"></td></tr>
    <input type="text" name="school_name_1" value="" placeholder="Your School Name"></td></tr>
    <tr><td></td><td><input type="text" name="stu_id_1" value="" placeholder="Your Student ID/Roll"></td></tr> 
    <tr><td></td><td>
      <select name="class_1" id="class" required >
        <option selected="selected" value="">Please Select Your Class</option>
        <option value="Six">Six</option>
        <option value="Seven">Seven</option>
        <option value="Eight">Eight</option>
        <option value="Nine">Nine</option>
        <option value="Ten">Ten</option>
      </select> 
    </td></tr>
    </td><td>
    <select name="division_1" id="division" required>
      <option selected="selected" value="">Please Select Your Division</option>
      <option value="Dhaka">Dhaka</option>
      <option value="Chittagong">Chittagong</option>
      <option value="Sylhet">Sylhet</option>
    </select> 
    </td></tr>
    <tr><td></td><td><input type="text" name="mobile_1" value="" placeholder="Your Parent's Mobile" required id="phone" ></td></tr>
    <tr><td></td><td><input type="text" name="interest_1" value="" placeholder="Your Interest e.g.: Robotics, Physics, Chemistry, Biology "></td></tr>
    <tr><td></td><td><textarea name="address_1" required id="must"="required id="must"" placeholder="Your Full Residential Address"></textarea></td></tr>                                   
    <tr><td></td><td><input type="text" name="email_1" value="" placeholder="Your Email Address" id="email_1"  ><img id="tick_1" src="tick.png" width="16" height="16"/>
    <img id="cross_1" src="cross.png" width="16" height="16"/></td></tr>
</table>
<br>
<p class="submit"><input type="submit" name="commit" value="Register" ></p><br>
<label>
  <div align="center"><a href="http://ignite-bd.com/submit-concept-paper/" target="_blank"><strong>Upload your Concept Paper within 3 weeks (21 Days) to qualify for the divisional round</strong> </a>
  </div>
</label>
<br><br>            
</form>

， javascript验证函数如下:

function idea_1_check()
{
  var stu_name=document.forms["idea_1"]["stu_name_1"].value;
  var school=document.forms["idea_1"]["school_name_1"].value;
  var id=document.forms["idea_1"]["stu_id_1"].value;
  var mob=document.forms["idea_1"]["mobile_1"].value;
  var add=document.forms["idea_1"]["address_1"].value;
  var email=document.forms["idea_1"]["email_1"].value;
  var atpos=email.indexOf("@");
  var dotpos=email.lastIndexOf(".");   
  if (stu_name==null || stu_name=="" || stu_name.length<6)
  {
    alert("Please provide Your full name");
    return false;
  }
  if (school==null || school=="" || school.length<6)
  {
    alert("Please provide Your full School name");
    return false;
  }
  if (id==null || id=="" || id.length<1)
  {
    alert("Please provide Your Roll/ID");
    return false;
  }
  if (add=null || add=="" || add.length<10)
  {
    alert("Please provide Your full Residential Address");
    return false;
  }
  else if (email==null || email=="")
  {
    alert("Email must be filled out.");
    return false;
  }
  else if (atpos <1 || dotpos <atpos+2 || dotpos + 2 >= email.length)
  {
    alert("Not a valid e-mail address");
    return false;
  }
}

一切看起来都很好。但是验证不起作用。相同的代码与另一个类似的工作。那么我的代码有什么问题?