Here is some code to create your input box:

var element = document.createElement('input');

element.type = 'hidden';

element.value = '';

element.id = '';

To add it to a <form> with id=myform you could do this:

var myform = document.getElementById('myform');

myform.appendChild(element);

FYI: Your <input> doesn't have a name attribute. If you're planning on submitting it as part of a form and processing it on the server side, you should probably include one.