Having played with this a couple days:

1. there's no need for the welcome pop-up every time.

2. the player timing is not good. Are you randomizing durations as a stylistic choice to sound like a first day piano player? it frequently runs together 3 or 4 notes 1/32nds so i have to play it 3 or 4 times to hear the notes with something approximating an appropriate duration.

3. when making a mistake - if you're playing on a keyboard, i can see value on starting over from the beginning. but if you're clicking on the mouse, it's kind of pointless.

That's very nice. I used to do http://perfectpitchpuzzle.com daily, which is similar but shorter and with wordle mechanics.

I don't know how other people do these things but I've got my keyboard next to my computer so that's where I work it out and the number of attempts (that you know about) isn't meaningful. But it's still great practice.

Nice job. Having built a couple of play-by-ear training games, my recommendation would be to add support for MIDI controllers. If you use the WebMIDI.js project, it should be relatively easy to set up.

https://github.com/djipco/webmidi

The game is client side, and the stats are stored in a tiny Pocketbase instance. Ensuring the stats aren't spammed is an interesting problem with a client side browser game. If it becomes a problem I might look into a server issued token solution.