If you want to quickly delete all branches visible on one page in GitHub (e.g. stale branches) this script will click all those bucket buttons for you.

delete_branches_on_page.js

// Self executing loop staggered with delete requests to deal with local GH js rerenders
// Experiment with the timedelay of 1000 by default
var buttons = Array.from(document.querySelectorAll('button[title^="Delete "]'));
function loopIt(x) { 
  setTimeout(() => {
    buttons[x].click();
    if(x < buttons.length -1) loopIt(x+1);
  }, 1000);
};
loopIt(0);

Just execute that script line in the browser console on the page you are looking at ... and with the automatic reload all you need to do is click up and Enter again till you are through with all the branches!

Updated the script to deal with the UI lock by GitHub