Quickly review files in Github pull requests by pressing spacebar on your keyboard with this userscript.

userscript-github-pull-request-autofocus.js

// ==UserScript==
// @name         Github Pull Request Autofocus
// @description  Helps you quickly review files in Github pull requests.
// @author       Jake Bellacera
// @match        https://github.com/*/pull/*/files
// ==/UserScript==

// HOW TO USE
// ==========
// 1. Open a Github pull request.
// 2. Navigate to the "Files changed" tab.
// 3. Click on one of the "Viewed" checkboxes on top of any file to mark it as viewed and collapse
//    the diff. At this point the next file's "Viewed" checkbox will be focused.
// 4. View the changes on the next file, then press your space bar key to check the file's "Viewed"
//    checkbox.
// 5. Repeat these steps for each file.
//
// TROUBLESHOOTING
// ===============
// Github dynamically loads pages onto the screen, so your userscript extension may not notice that
// you navigated to the "Files changed" page. If the script isn't working just reload the page.

(function () {
  "use strict";

  const checkboxSelector = ".js-reviewed-checkbox";

  const focusNextCheckbox = () => {
    const allCheckboxes = Array.prototype.slice.call(
      document.querySelectorAll(checkboxSelector)
    );
    const nextCheckbox = allCheckboxes.find((checkbox) => !checkbox.checked);

    if (nextCheckbox) {
      nextCheckbox.focus();
    }
  };

  document.addEventListener("change", (e) => {
    if (e.target.matches(checkboxSelector)) {
      if (e.target.checked === true) {
        focusNextCheckbox();
      }
    }
  });
})();