Browser-side JavaScript cannot send email on its own. The best it can do is try to open the user's email application for them so they can send the email. For example:
location.href = 'mailto:' + encodeURIComponent(emailAddress) +
'?subject=' + encodeURIComponent(subject) +
'&body=' + encodeURIComponent(body);
You could hook the submit event of the form, prevent the default action, and execute that code, and the end result would be they could fill out the form, click submit, their email client opens, and they can click send.