Very good question.
It is not the best resource, but it is the best one for total beginners especially ones who have 0 experience in programming, I usually start teaching my students who know only basics of HTML and CSS using w3schools program. It has short, clear description and examples.
P.S. w3schools is NOT related to W3C.
This is the #1 reference for any JS developer from beginners till very experienced ones. Go though each section, each article, each example. Go though each Object, each API, each method, each parameter. I promise you will find a lot of small tricks or cool functions you never heard about.
For example, one day I randomly was browsing Element documentation and found Element.getBoundingClientRect(). So you can find element's position in viewport in 1 line of Vanilla JS without any jQuery, it's cool, isn't it? And that was not the only one example...
You can register, contribute, translate MDN knowledge base!
This is a solid starting point for everyone who was working with jQuery. Today it is still very useful resource even for those who never used jQuery because it contains all the main JavaScript functions from AJAX till DOM manipulation in one place.
The best way to learn is to see how others are coding. Go to GitHub and browse the source code of many JavaScript projects.
Awesome blog about how to program JavaScript itself. Want to change what 'instanceof' do or what happens if property on object doesn't exists?
And many links available here:
P.S. I am available on both and on Hashnode's. If you will need something, feel free to ask @mevrael
Just open DevTools and go experimenting!
P.S. I also recommend to dig into the history of JavaScript, asynchronous programming, Web Standards, HTTP, UI development, DOM, events, accessibility and software engineering and architecture in general.