I found a fairly elegant solution (or hack, whatever fits) for Prototype.JS users, being one of the last holdouts using Prototype. A simple substitution of corresponding jQuery methods should do the trick.
First, make sure there's a <form> tag, and a submit button with a class name that can be referenced later (in this case faux-submit) that is nested inside an element with a style set to display:none, as illustrated below:
<form id="login_form" action="somewhere.php" method="post">
<input type="text" name="login" />
<input type="password" name="password" />
<div style="display:none">
<input class="faux-submit" type="submit" value="Submit" />
</div>
<button id="submit_button">Login</button>
</form>
Then create a click observer for the button, that will "submit" the form as illustrated:
$('submit_button').observe('click', function(event) {
$('login_form').submit();
});
Then create a listener for submit event, and stop it. event.stop() will stop all submit events in the DOM unless it's wrapped in Event.findElement with the class of the hidden input button (as above, faux-submit):
document.observe('submit', function(event) {
if (event.findElement(".faux-submit")) {
event.stop();
}
});
This is tested as working in Firefox 43 and Chrome 50.