How to listen to submit event

Add-ons Development
#1

I am still stuck in this problem that I posted earlier Can’t listen to submit event. I looked at the events reference in the MDN. I found the submit event in Submit. There is something I do not get which says:

Note that submit is fired only on the form element, not the button or
submit input. (Forms are submitted, not buttons.)

My HTML form has the submit as input:
<input type="submit" id="submit-button" value="Add">

And the script file is trying to listen to it. The full codes are posted aleady in this post

Can you please clarify the quoted text:

Note that submit is fired only on the form element, not the button or
submit input. (Forms are submitted, not buttons.)

#2

As I have answered for your other question, you need to listen for the submit event on the <form> element, not the input.