How to prevent form submission while using HTML5 client-side form validation in Opera 11?

Question

How to prevent form submission while using HTML5 client-side form validation in Opera 11?

Here is a sample test page:

Validation works in Opera 11, but when the button is clicked after entering a value, the browser submits the form.

I want the browser to stay on the webpage always, which is good for client-side-only scripts, on the local hard drive, where there is no server, for example.

When I add return false; or try to prevent the form from submitting, the validation no longer works.

Opera 11.10 Build 2092

EDIT:

Thanks to robertc's solution, I got it working. Here is the test page without jQuery.

 (function() {
   "use strict";

   window.addEventListener("load", function() {
     document.getElementById("testForm").addEventListener("submit", function(event) {
       event.target.checkValidity();
       event.preventDefault(); // Prevent form submission and contact with server
       event.stopPropagation();
     }, false);
   }, false);
 }());

<section>
  <h2>Test</h2>
  <form id="testForm">
    <input type="text" name="test" id="test" required/>
    <input type="submit" value="Test" />
  </form>
</section>

Answer 1

OK, try this. The form is basically as before:

<section>
    <h2>Test</h2>
    <form id="form">
        <input type="text" name="test" id="test" required/>
        <input type="submit" value="Test"/>
    </form>
</section>

Then bind the submit event to a function which calls the checkValidity() method:

function manualValidate(ev) {
    ev.target.checkValidity();
    return false;
}
$("#form").bind("submit", manualValidate);