Pre-fill email with form data

I am looking to have an HTML form that, using only JS/jQuery (no PHP), takes data from a "subject" and "message" field, and sends an email. I do not want the server to send the email, as HTML and JS are client-side, not server-side. Again, no PHP.

However, I do want it to open the users mail client but have the subject and body pre-filled with the form data, and the to field prefilled with my email address. Essentially, I need a more advanced mailto:test@test.com.

Here is my contact form so far:

<h2>Send a message</h2>
<form id="sendmsg">
    <div class="field">
        <label for="subject">Subject</label>
        <input type="text" name="subject" id="subject" value="" />
    </div>
    <div class="field">
        <label for="message">Message</label>
        <textarea name="body" id="body" rows="6"></textarea>
    </div>
    <ul class="actions">
        <li><input type="submit" id="submit" value="Submit" /></li>
    </ul>
</form>

I have tried several attempts such as this (in jQuery):

<script>
    $(document).ready(function() {
        $('#submit').click(function() {
            $('#sendmsg').attr('action', 'mailto:contact@test.com?subject=' + $('#subject').val() + '&body=' + $('#body').val());
            $('#sendmsg').submit();
        });
    });
</script>

Help is appreciated, thanks!