Scroll to current file for GitHub

scroll-to-current-file-for-github.user.js

// ==UserScript==
// @name        Scroll to current file for GitHub
// @match       https://github.com/*
// @version     1.0
// ==/UserScript==

function check(callback) {
  const result = callback();
  if (!result) {
    throw new Error("assertion Failed: "+ callback.toString());
  }

  return result;
}

function getRefName() {
  const embeddedData = check(() => document.querySelector('script[data-target="react-app.embeddedData"]'));
  const obj = JSON.parse(embeddedData.text);
  const refName = check(() => obj?.payload?.refInfo?.name);
  return refName;
}

function trimPrefix(str, prefix) {
  check(() => str.startsWith(prefix));
  return str.substring(prefix.length);
}

function scrollToCurrentFile() {
  const pathname = location.pathname;
  const [_empty, _owner, _repo, type, ...rest] = pathname.split("/");
  if (type != "blob" && type != "tree") {
    return;
  }

  const restPath = rest.join("/");
  const refName = getRefName();
  const filePath = trimPrefix(restPath, refName);
  if (!filePath) {
    return;
  }

  const relativePath = trimPrefix(filePath, "/");
  const item = document.getElementById(`${relativePath}-item`);

  item?.scrollIntoView({ block: "center", behavior: 'smooth' });
}

// After page load
window.addEventListener("turbo:load", scrollToCurrentFile);

// File tree click
document.addEventListener("soft-nav:end", scrollToCurrentFile);

// Window resize
let handle = null;
window.addEventListener("resize", function () {
  // debounced resize handle
  if (handle != null) {
    clearTimeout(handle);
  }

  handle = setTimeout(function() {
    handle = null;
    scrollToCurrentFile();
  }, 200);
});