A friend wants to learn JavaScript – Which are the best free courses?

For someone who has never coded before, I would still recommend Codecademy: https://www.codecademy.com/learn/introduction-to-javascript

It certainly depends on what their goal is afterwards, is it to go into frontend webdev like React or just learning JS as an intro to computer science in general? There's going to be a jump from coding in Codecademy tutorials to building a project from scratch, but I think their interactive interface is very friendly for beginners.

This might help: https://javascript.info/

Grasshopper is a mobile app that teaches programming concepts. It is basically JS syntax and semantics. For someone new to programming in general, this is what I suggest. It has a great curriculum and is easier for the unexperienced to start with and see if programming is a fit and interesting to them.

Depends if they know any other programming language. As a programmer coming from another language I found the course by Mosh is really good. Also I think the web dev simplified YouTube channel is a good resource.

freecodecamp is a pretty decent resource.

Freecodecamp on YouTube