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);

Updated the script to deal with the UI lock by GitHub