Will Adams WillAdamsDotDev
My First Browser Extension

My First Browser Extension

The problem 😕

As someone who answers students’ questions in Brad Traversy’s courses, I’ve noticed that many of them were reporting having difficulty keeping track of which lesson they’re on in the side menu while using the course platform, as each time they would click on a lesson the side menu would reset.
Additionally the video player is currently limited to a maximum width of 1356px, meaning for those students on larger monitors, the video looks oddly small.
Unfortunately, since the platform is provided by Kajabi, we don’t have access to their code to modify the behavior.

Before extension:

Before Extension

The solution 💡

To address this issue, I’ve developed a browser extension for Chrome and FireFox. This extension is a simple yet effective add on that automatically scrolls the active lesson to the center of the sidebar and highlights it in Traversy Media blue, each time a lesson is selected.
It also targets the video container (Ironically with the class name kjb-video-responsive 🤷) and maximises it to the available space in the viewport while limiting the max size so all the video is always visible and preserving the aspect ratio.

As a newcomer to browser extension development, creating this tool was a great learning experience for me. It was a simple introduction to the process of developing browser extensions, and I found it to be an enjoyable and rewarding process.

After extension:

Before Extension

Resources I used 📚

Super simple 💪

The code itself to implement this part of the extension is only 28 lines:

const videoWrapper = document.querySelector('.kjb-video-responsive')

function highlightAndScrollIntoViewActive() {
  const sideMenu = document.querySelector('.main-sidebar')

  /** @type HTMLLinkElement */
  const activeLink = sideMenu.querySelector('.product-outline-post.active')
  activeLink.style.outline = '3px solid #0060df'
  activeLink.style.padding = '6px'

  activeLink.scrollIntoView({ behavior: 'smooth', block: 'center' })

function maximiseVideo() {
  const searchForm = document.querySelectorAll('form[role=search]')[1]
  videoWrapper.style.maxWidth = '100%'
  videoWrapper.style.paddingBottom = '0'
  videoWrapper.style.aspectRatio = '5/4'
  videoWrapper.style.height = 'auto'
  videoWrapper.style.maxHeight = `calc(100vh - ${
  videoWrapper.style.width = '100%'


// NOTE: Ensure scroll animation runs after video resized

All it does is use the active class that Kajabi add to find the correct element in the side bar, scroll it into view and add an outline to highlight it.
Any time a student clicks a lesson it’s a link that takes them to a page for that lesson, so the code runs again after the DOM is loaded (this is the default for any extension).

For maximising the video size I noted that Kajabi were using the old trick of height: 0; and padding-bottom: 56%; to preserve the aspect ratio, but also limiting the max-width to 1356px. Using newer css features like CSS Aspect Ratio helped to fix this along with calculating the max height to account for the search bar they position above the video.

An update: Persisting Video Speed

I have further enhanced the extension to include a feature that allows the video speed to be saved to local storage and be restored for subsequent lessons. This enhancement posed a challenge as the video speed settings are dynamically inserted into the DOM after the video has loaded. My solution? The MutationObserver API.

Here is the code to persist the video speed:

/** @param {number} indx */
function handleSpeedSettingClick(indx) {
  return function () {
    localStorage.setItem('playback-speed', `${indx}`)

function getSpeedSettingCheckBoxes() {
  /** @type {NodeListOf<HTMLInputElement>} */
  const speedSettingCheckBoxes = document.querySelectorAll('input[name=Speed]')
  return speedSettingCheckBoxes

/** @param {NodeListOf<HTMLInputElement>} speedSettingCheckBoxes*/
function addSpeedSettingsEventListeners(speedSettingCheckBoxes) {
  // add event listeners
  speedSettingCheckBoxes.forEach((checkBox, indx) => {
    checkBox.addEventListener('click', handleSpeedSettingClick(indx))

/** @param {NodeListOf<HTMLInputElement>} speedSettingCheckBoxes*/
function restoreSpeed(speedSettingCheckBoxes) {
  const storedSpeed = localStorage.getItem('playback-speed')
  if (storedSpeed) {
  // close settings if open
  if (isSettingsOpen()) getSettingsButton().click()

function getSettingsButton() {
  /** @type {HTMLButtonElement} */
  const settingsButton = document.querySelector(
    'button[aria-label="Show settings menu"]'
  return settingsButton

function isSettingsOpen() {
  return getSettingsButton().getAttribute('aria-expanded') === 'true'

function handlePlayback() {

// NOTE: video settings are dynamically inserted into DOM after wista loads the
// video.

// only add speed setting event listeners once
let needToAddSpeedSettingListeners = true
let settingsOpenedFirstTime = false
// only add one playback event listener
let playbackListenerAdded = false

/** @param {Array<MutationRecord>} mutationList*/
function mutationCallback(mutationList) {
  mutationList.forEach(() => {
    // need to open and close the settings to apply
    const settingsButton = getSettingsButton()

    if (settingsButton && !settingsOpenedFirstTime) {
      // open settings
      settingsOpenedFirstTime = true

    const speedSettingCheckBoxes = getSpeedSettingCheckBoxes()

    // check that the speed settings are there and we can set speed
    if (
      speedSettingCheckBoxes &&
      needToAddSpeedSettingListeners &&
      speedSettingCheckBoxes.length === 7
    ) {
      needToAddSpeedSettingListeners = false

    // FIX: Kajabi resets playback speed to 1 on first play of video
    const video = document.querySelector('video')
    if (video && settingsButton && !playbackListenerAdded) {
      video.addEventListener('playing', handlePlayback)
      playbackListenerAdded = true

const observerOptions = {
  childList: true,
  subtree: true,

const mutationObserver = new MutationObserver(mutationCallback)

mutationObserver.observe(videoWrapper, observerOptions)

This code uses the MutationObserver API to watch for changes to the DOM. When the speed setting buttons are inserted into the DOM, the mutationCallback function is called. This function then adds event listeners to the speed setting buttons to set the users chosen speed in local storage and restores the previously saved video speed.

Get it if you’re a student of Traversy Media 🚀

The Scroll Active Lesson extension is available for both Chrome and Firefox browsers, and it’s easy to use. You can install the extension for Chrome from the Chrome Web Store and for Firefox from the Firefox Add-ons store.

This extension is designed to improve the student experience by making it easier for them to keep track of their progress in the course. By automatically scrolling the active lesson to the center of the sidebar and highlighting it, students can save time and frustration and focus on learning.

If you want to learn more about the extension or contribute to its development, the source code is available on Github. Feel free to submit issues or pull requests if you encounter any problems or have any suggestions.