Freecodecamp
Freecodecamp offers a lot of small Javascript lessons. This can be a bit daunting to get started with. So don’t expect to finish this in a few hours. But going through the whole curriculum not only will teach you the full scope of the Javascript Language but also will allow you to receive certifications which are accepted in certain tech companies as a valid substitute for a computer science degree.
Codecademy
Codecademy also offers Javascript lessons but they do require you to create an account for them. Lessons 1-9 will learn you most if not all of the concepts you will need for the game development workshops. Further lessons are still useful if you are interested in learning more about web development in general. The website is set up as a business though so more advanced tuturials might be locked after a paywall.
Mozilla
The Mozilla reference on Javascript is in my opinion the most complete and easiest to navigate. The information here is likely more suited for people who have previous experience with programming.
Google/YouTube
There is a lot of material out there on the internet just one search away. Be curious and you will surely find something that fits your needs.