Send simple HTTP request with HTML submit button

I have added a submit button to the index.html page that resides on my server side

<form method="get" action="/start">
    <h5>Start Ad-Placer!</h5>
    <input type="submit" value="Start">
</form>

I need the button to simply send a http request to http://127.0.0.1:8484/get/start to start some process. Then once the process is done after a few seconds, I need to simply display an alert message with the response message, acknowledging it is done.

How can I do that with minimum efforts (without using JQuery or other libraries).