Prevent Double Form Submission

I want to add code that will prevent the submit button from being clicked more than once before it POSTS. The current code just disables the button when it is clicked, but I want it to immediately disable the button and then submit the form. Current Code: <form action="#" method="post" name="message_frm"> <div class="box-header" > <h2>Group Messaging</h2> </div> <div class="input-group"> <span id="aln" class="input-group-addon">Message:</span> <textarea style="height:195px;" onkeyup="check_left([login to view URL])" name="message" id="message" class="form-control" ></textarea> <span class="input-group-addon"></span> </div><br> <button style="float:right;" type="submit" class="btn btn-primary" onclick="this.disabled=true">Send Message</button> </form> If I accept you as the freelancer, I will send you the entire file.