You’re probably looking for confirm(), which displays a prompt and returns true or false based on what the user decided:

if (confirm('Are you sure you want to save this thing into the database?')) {
  // Save it!
  console.log('Thing was saved to the database.');
} else {
  // Do nothing!
  console.log('Thing was not saved to the database.');
}

You can easily do it with a confirm onclick:

Copy<p id="accept-favor"><a title="Accept this Favor" 
  href="?wp_accept_favor=<?php comment_ID(); ?>" 
  onclick="return confirm('Are you sure you would like to accept this reply as your favor?');"
  >Accept this Favor</a></p>

Though this will say OK/Cancel instead of Yes/No. If you really want Yes/No, you'll have to use a custom dialog.

You basically just need to bootstrap myFunction, and also place the prompts inside the myFunction so they get called again if the confirmation is false.

eg.

function myFunction() {
  var name = prompt('What is your name?');
  var conf = confirm('Is your name: ' + name);
  if (conf === true) {
    alert("You pressed OK!");
  } else {
    alert("Input your correct name");
    myFunction();
  }
}

myFunction();