Delete stale branches from the GitHub repo's stale branches page (github.com/user/repo/branches/stale). Originally from https://stackoverflow.com/a/30789283

github-delete-stale-branches.js

// Paste in browser console and run

async function deleteStaleBranches(delay=500) {
    var stale_branches = document.getElementsByClassName('js-branch-delete-button');
    for (var i = 0; i < stale_branches.length; i++)
    {
        stale_branches.item(i).click();
        await new Promise(r => setTimeout(r, delay));
    }
}

(() => { deleteStaleBranches(500); })();