Confirm before a form submit

Question

I have searched for an answer but couldn't find one!

I have a simple form,

<form action="adminprocess.php" method="POST">
    <input type="submit" name="completeYes" value="Complete Transaction" />
</form>

How would I adjust this to confirm before processing the form?

I tried onclick, but couldn't get it working.

Any ideas?

UPDATE - What I now have.

<script type="text/javascript">
var el = document.getElementById('myCoolForm');

el.addEventListener('submit', function(){
return confirm('Are you sure you want to submit this form?');
}, false);
</script>

<form action="adminprocess.php" method="POST" id="myCoolForm">
     <input type="submit" name="completeYes" value="Complete Transaction" />
</form>

Answer 1

HTML:

<form action="adminprocess.php" method="POST" id="myCoolForm">
    <input type="submit" name="completeYes" value="Complete Transaction" />
</form>

JavaScript:

var el = document.getElementById('myCoolForm');

el.addEventListener('submit', function(){
    return confirm('Are you sure you want to submit this form?');
}, false);

Edit: you can always use inline JS code like this:

<form action="adminprocess.php" method="POST" onsubmit="return confirm('Are you sure you want to submit this form?');">
    <input type="submit" name="completeYes" value="Complete Transaction" />
</form>

Answer 2

<input type="submit" onclick="return confirm('Are you sure you want to do that?');">