What's the best resource for existing programmers to learn JavaScript?

MDN is always a valuable resource, especially if you are interested in the JavaScript language itself or in web frontend development.

https://developer.mozilla.org/en-US/docs/Web/JavaScript

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guid...

I wrote my JavaScript book for people who already know how to program – maybe it works for you. Free to read online: https://exploringjs.com/impatient-js/

I liked Wes Boss’ js for beginners course. My favorite part was that he was basically trying out the concept and showing how the language works by experimentation.

I have written a lot of JS but this approach brought needed clarity about the inner workings of the language.

Mate, "learn JS" is a little too vague. There is A LOT in the JS world so you need to narrow down your focus. It depends on what youre doing but reading docs, youtube, udemy, blogs, freecodecamp, theodinproject. all great resources.

The Helsinki MOOC is great and was just upgraded to JS.

https://fullstackopen.com/en/

I've always liked https://javascript.info/