I am actually learning JS, but much basic stuff. I'm using freecodecamp. I personally prefer "type on the browser following written instructions" than videos.

I am actually learning JS, but much basic stuff. I'm using freecodecamp. I personally prefer "type on the browser following written instructions" than videos. Pace on video is very hard to set right. I only checked the first and second lessons, but I did like your tool! As I can type while the voice is still talking, I can move faster if i want. And listen to instructions while highlighting the part of the code on the screen felt natural. So I think you are on to something and you can have the best of both worlds, clear instructions that stick on your brain and flexibility to follow anyone's pace. The features I would ask: i) allow me to click at the bar of the bottom and go back (or forward) to the part of the audio that I want to read. ii) mark at the bar the exact moment where you objectively explain the key concepts of the class (and make sure at each lesson you have one sentence that explains each concept very directly, like "render function is.."). good luck!! Sounds very promising! :) Example