How can I void a form action and execute jQuery when all HTML form elements are validated?

Question

I have a simple HTML form that I want to leverage for required field validation. My issue is that I want to use the HTML5 form validation BUT at the same time avoid actually submitting the form because I want to execute a jQuery Ajax call instead. I know you can disable html5 validation, but I want to keep this as my primary method of form validation instead of a jQuery plugin.

Any thoughts?

HTML

<form action="donothing" id="membershipform" method="get" accept-charset="utf-8">
    <input type="text" class="borderr3 innershadow3" name="some_name" value="" id="some_name" placeholder="first and last name" required>
    <input type="email" class="borderr3 innershadow3" name="some_name" value="" id="some_name" placeholder="email" required>
    <input type="phone" class="borderr3 innershadow3" name="some_name" value="" id="some_name" placeholder="phone" required>    
    <input type="phone" class="borderr3 innershadow3" name="some_name" value="" id="some_name" placeholder="mailing address" required>      
    <input type="phone" class="borderr3 innershadow3" name="some_name" value="" id="some_name" placeholder="how you heard about us" required>
    <p>
        <input type="submit" id="submitbtn" class="submitbtn" value="Continue" style="width:265px">
    </p>
</form> 

JavaScript:

$(function(){
  $("#submitbtn").click(function(){
    $.ajax({
      url: "<?php bloginfo('template_url') ?>/ajax-membership.php",
      success: 
      function(txt){
        if(txt){
          $("#thankyou").slideDown("slow");
        }
      }
    });
  });
});

Answer 1

According to this: Do any browsers yet support HTML5's checkValidity() method?, and this may not be the latest truth since HTML5 is a work in progress, the Form.checkValidity() and element.validity.valid should let you access validation information from JavaScript. Assuming that's true, your jQuery would need to attach itself to the form submit and make use of that:

$('#membershipform').submit(function(event){
    // cancels the form submission
    event.preventDefault();

    // do whatever you want here
});