Are there decent tools to debug and check JS for you, so that you don't have to rely on the browser built-in support (which is incredibly forgiving but also doesn't tell you what is going on)?
A massive advantage of BASIC was that it would tell you it was wrong as soon as you typed something with a syntax error in it, and it put a big flashing "?" (or similar) right there until you fixed it. Can JS be made to do that?
I've thought a few times that this is the modern equivalent of the immediate feedback "plot via BASIC".
It's even better, given the fact that JS is a decent language and the results are more easily shareable with your friends.