I don't how it posible can you Help me?

I don't how it posible can you Help me?

  1. How to select auto form name?
  2. How to select auto input id or name?
  3. How to submit and reset on my page in my iframe?
  1. <iframe id="myiframe" width="400" height="300" src="http://localhost/wordpress/wp-login.php?action=register"></iframe>
  2. <button id="btnTest">Fill the form</button> <button type="submit" id="submit">Submit</button>
  3. <button type="reset" id="reset">Reset</button>
  4.   <script>    
  5.      function load() {
  6.          var btn = document.getElementById('btnTest');
  7.         btn.onclick = function(){
  8.         var ifrm = document.getElementById('myiframe');
  9.         ifrm.contentWindow.document.forms['registerform'].user_login.value = 'yourname';
  10.         ifrm.contentWindow.document.forms['registerform'].user_email.value = 'examplae@email.doamin';
  11.      };    
  12.    }
  13.    window.onload = load;
  14.   </script>