I would like to make a 2d game using plain Javascript this coming weekend. What do you suggest?

Html and css

to google and read about game mechanics, and mathematics for games.

Tic tac toe?

Make somethin like Facebook but better instead

@Stuxnet
Who told you about my Chinese Facebook 😮

@SortOfTested New Facebook?

Mother fuck....jiiiann yaaaaaang

Why use plain js, and not a library like p5.js or three.js, which would be easier and have have a bunch of tutorials.

@MrNitrogen agreed, p5.js is a great one

One div = one pixel

@MrNitrogen obviously he needs two.js

Does WebGL count as "plain javascript" since its integrated into browsers and not an external library?

If so, look into WebGL, which is just a wrapper for OpenGL accessible from a browser through javascript.

It's the closest and most performant (as far as I know) way to drawing things on screen.

Though if you don't want to struggle with a lot of boilerplate code look for an engine. I believe RayLib has a .js extension

make a game that has physics in it. like gravity and stuff