Absolutely valid.

    <form action="javascript:alert('Hello there, I am being submitted');">
        <button type="submit">
            Let's do it
        </button>
    </form>
    <!-- Tested in Firefox, Chrome, Edge and Safari -->

So for a short answer: yes, this is an option, and a nice one. It says "when submitted, please don't go anywhere, just run this script" - quite to the point.

But ... !

Why don't we take this to the next level - let the event handler know which form we're dealing with! Here's how to do it. (Note how the first form, no matter how obvious, won't do the job. We need a few keystrokes more.)

    <form action="javascript: myFunction( this ) ">  
    <!-- But this won't work -->

    <form action="javascript:;" onsubmit=" myFunction( this ) ">  
    <!-- Tadaammm! -->

Now you can access the sender form properly. (You can write a simple "#" as action, it's quite common - but it has a side effect of scrolling to the top when submitting.)

Again, I like this approach because it's effortless and self-explaining. No "return false", no jQuery/domReady, no heavy weapons. It just does what it seems to do. Surely other methods work too, but for me, this is The Way Of The Samurai.

A note on validation

Forms only get submitted if their onsubmit event handler returns something truthy, so you can easily run some preemptive checks:

    <form action="/something.php" onsubmit=" return isMyFormValid ( this ) ">

Now isMyFormValid will run first, and if it returns false, server won't even be bothered. Needless to say, you will have to validate on server side too, and that's the more important one. But for quick and convenient early detection this is fine.

First of all, you want instead of what you got now. Then your function ajaxSubmit looks like this: function ajaxSubmit(form) { // Serialize form for (var data = [], elems = form.elements, e = 0; e < elems.length; e++) { // do not serialize disabled elements, unchecked radio/checkbox inputs or buttons if (/submit|image|reset/.test(elems[e].type) || (/checkbox|radio/.test(elems[e].type) && !elems[e].checked) || elems[e].disabled) continue; // serialize if (elems[e].options) { data.push(encodeURIComponent(elems[e].name) + '=' + encodeURIComponent(elems[e].options[elems[e].selectedIndex].value)) } else { data.push(encodeURIComponent(elems[e].name) + '=' + encodeURIComponent(elems[e].value)) } } var formUrl = form.action + '?' + data.join('&'); // now make that AJAX request (I guess you can do that yourself), return false on error return true; }

You cannot invoke JavaScript functions in standard HTML attributes other than onXXX. Just assign it during window onload.

<script type="text/javascript">
    window.onload = function() {
        document.myform.action = get_action();
    }

    function get_action() {
        return form_action;
    }
</script>

<form name="myform">
    ...
</form>

You see that I've given the form a name, so that it's easily accessible in document.

Alternatively, you can also do it during submit event:

<script type="text/javascript">
    function get_action(form) {
        form.action = form_action;
    }
</script>

<form onsubmit="get_action(this);">
    ...
</form>