Center horizontal scroll bar

Auto center the horizontal scroll bar

You will need to install an extension such as Tampermonkey, Greasemonkey or Violentmonkey to install this script.

You will need to install an extension such as Tampermonkey or Violentmonkey to install this script.

You will need to install an extension such as Tampermonkey or Violentmonkey to install this script.

You will need to install an extension such as Tampermonkey or Userscripts to install this script.

You will need to install an extension such as Tampermonkey to install this script.

You will need to install a user script manager extension to install this script.

(I already have a user script manager, let me install it!)

You will need to install an extension such as Stylus to install this style.

You will need to install an extension such as Stylus to install this style.

You will need to install an extension such as Stylus to install this style.

You will need to install a user style manager extension to install this style.

You will need to install a user style manager extension to install this style.

You will need to install a user style manager extension to install this style.

(I already have a user style manager, let me install it!)

// ==UserScript==
// @name         Center horizontal scroll bar
// @version      0.2.0
// @description  Auto center the horizontal scroll bar
// @author       dragonish
// @namespace    https://github.com/dragonish
// @license      GNU General Public License v3.0 or later
// @match        *://*/*
// @grant        none
// ==/UserScript==

(function () {
  const debounced = {
    timer: {},
    debounce(key, func, delay, immediate) {
      window.clearTimeout(this.timer[key]);
      if (immediate) {
        if (this.timer[key] === undefined) {
          func();
        }
      }
      this.timer[key] = window.setTimeout(() => {
        func();
        this.timer[key] = undefined;
      }, delay);
      return {
        cancel: () => {
          window.clearTimeout(this.timer[key]);
          this.timer[key] = undefined;
        }
      };
    }
  };
  function scroll(msg) {
    console.log(msg);
    window.scrollTo({
      left: (document.documentElement.scrollWidth - document.documentElement.clientWidth) / 2
    });
  }
  window.addEventListener('load', () => {
    setTimeout(() => {
      scroll('window loaded, try rolling.');
    }, 0);
  });
  window.addEventListener('resize', () => {
    debounced.debounce('scroll', () => {
      scroll('window resized, try rolling.');
    }, 250);
  });
})();