JS中的form.submit()不能提交表单的错误原因

<div id="register">
     <h4>会员注册</h4>
     <div class="formdiv">
         <form method="post" action="register.php?action=register" name="register" id="registerForm">
             <dl>
                 <dt>请认真填写以下内容</dt>
                 <dd class="hasspan">
                     用户名：<input type="text" name="username">
                 </dd>
                 <dd class="hasspan">
                     密码：<input type="password" name="pwd">
                 </dd>
                 <dd class="hasspan">
                     确认密码：<input type="password" name="pwdagain">
                 </dd>
                 <dd id="tximg">
                     <img src="img/face/m01.gif" alt="选择头像" id="faceimg">
                     <input type="hidden" name="touxiang" value="">
                     <label id="imgsrclabel">m01.gif</label>
                 </dd>
                 <dd style="margin-right:120px;">
                     验证码：<input type="text" name="code">
                     <span>
                         <img src="code.php" alt="code" id="code" name="code">
                         <a href="#code" id="change">换一张</a>
                     </span>
                 </dd>
                 <dd class="btns">
                     <input type="button" name="submit" id="submit" value="注册">
                     <input type="button" name="quit" id="quit" value="退出">
                 </dd>
             </dl>
         </form>
     </div>
 </div>
 

 /*注册表单提交*/
 function formDeal()
 {
     var btnSubmit = document.getElementById('submit');
     var formId = document.getElementById('registerForm');
     btnSubmit.onclick = function()
     {
         //表单的submit()方法不能提交表单
         formId.submit();
     }