[HTML / Javascript form] multiple submit buttons/actions | capturing submit action server side | alert before submit javascript may affect submit button on server side

example.html

Lets say you have a form, with multiple submit buttons:

<form method="POST">
<button type="submit" name="save">
  save
</button>
<button type="submit" name="send-all">
  send all
</button>
</form>

You wanna ask if the user is sure about the button they clicked on.

This works, it will prevent the submit and only submit the form if you confirm first.

But this will not send the button "send-all" as POST data, so if you plan to use in backend 
to differentiate action "save" from "send-all" you may have problems.

<script>
var send_all_button = document.getElementById("send-all");
send_all_button.addEventListener("click", function (event) {
  event.preventDefault();
  if ( confirm("Are you sure you wish to send all?") === false ) {
    return false;
  } else {
    this.form.submit();
  }
});
</script>

Solution:

Just use preventDefault() when user answer 'no'. Otherwise continue your action originate from 'send-all' button.

<script>
var send_all_button = document.getElementById("send-all");
send_all_button.addEventListener("click", function (event) {
  if ( confirm("Are you sure you wish to send all?") === false ) {
    event.preventDefault();
    return false;
  } else {
    return true;
  }
});
</script>