How to know which submit button fired the onsubmit event

When you have more than one submit button in a form, is there a way to know which one fired the onsubmit event without adding code to the buttons themselves?

Edit: I need to do the check on the client-side, i.e. with JavaScript.

Solution

There is a submitter attribute on SubmitEvent object.

See example:

<!DOCTYPE html>
<html>
<body>
<form action="./test.html" onsubmit="myFunction(event)">
  Enter name: <input type="text" name="fname">
  <button id="firstButton" type="submit">Button 1</button>
  <button id="secondButton" type="submit">Button 2</button>
</form>

<script>
function myFunction(event) {
  // This should log id of the button that was used for submition
  console.log(event.submitter.id); 

  // Prevent sending the form (just for testing)
  event.preventDefault();
}
</script>

</body>
</html>

See https://developer.mozilla.org/en-US/docs/Web/API/SubmitEvent/submitter