More and more developers are forgetting that some users won't load all or some of the script tags. I have people linking me stuff like this all the time, and all I see is a blank screen.
Using in Firefox browser on iPad and playing with four fingers. When I go to move all four fingers to change the pitch of all four notes this causes my iPad to attempt switch to a different app. When I then release all four fingers the notes I was playing 'stick' and continue to play. To stop them I have to refresh the page.
The point was more that the notes 'stick' after I return to the Firefox window. With four fingers playing the sounds can be a little wild. It took me a couple of tries to figure out why it had happened so I am guessing another user might be similarly confused.
Not to take anything away from this delightful little app. I just wanted to help out by reporting a little bug I found.
But with all of those turned down, there are some interesting shapes in the frequency view. Maybe some sort of stereo spread effect that get mixed to mono for the FFT display?
The former can be asked of any library / framework. Visit React's website to learn about why it's useful. Others have covered some reasons: it makes reasoning about applications easier and makes falling into composition of (mostly) stateless components the default
The latter is because people might be interested in seeing what's possible in React. Even viewing the page in React's dev tools is interesting and shows the author is also using Redux.
Seriously though, React and Typescript are both technologies some people prefer to work with, because they find it easier to be expressive/reason about their application's architecture. The 'point' usually boils down to that as far as I know.