How can I submit a form using JavaScript?

You can use...

document.getElementById('theForm').submit();

...but don't replace the innerHTML. You could hide the form and then insert a processing... span which will appear in its place.

var form = document.getElementById('theForm');

form.style.display = 'none';

var processing = document.createElement('span');

processing.appendChild(document.createTextNode('processing ...'));

form.parentNode.insertBefore(processing, form);

It works perfectly in my case.

document.getElementById("form1").submit();

Also, you can use it in a function as below:

function formSubmit()
{
    document.getElementById("form1").submit();
}

Set the name attribute of your form to "theForm" and your code will work.