I would like to get an Internship this summer (I’m 15) and need to know what are those things in JS all professional devs need to know?
Build something. This is the best advice you will ever get from anyone trying to teach you how to program. Pick something, anything: a game, a todo list, a simple email client; split the problem down into small steps; and then learn how to do each step by Googling it. I got this advice early on and didn't follow it. I spent time choosing the right programming language/framework and got distracted by ideas for one side project after another. I never finished anything for two years. Finally, I got frustrated with myself, quit my job, and sat down for 6 months to a built a simple web app. I learned so much building that web app that I was able to get my first job at a startup right after. Edit: If you want to learn how to build a game, I have a step by step example here: http://js.davidmiranda.info/ I taught people how to build this simple game as part of a 3 day class at my local library. I've been meaning to turn it into a series of blog posts, but haven't gotten around to it yet (this is all I have so far: http://smashingthingstogether.co...). For now, you can click through each example Codepen link and play around with the code to try to make it do what you want. There are some js tutorial links at the bottom that might benefit you too. Edit 2: I also recommend Wes Bos' courses — they're da bomb!
Creative Director, OpenStack Foundation
@alec_joness Components. React / Vue / etc. The particular frameworks and implementations will come and go, but thinking in components is really transformative to how you build and organize products. That said, I would definitely do a course or absorb as much vanilla JS as you possibly can before getting too far into any framework. Learn what the language does out of the box.
@alec_joness You need to be able to find answers that you don't know, and be humble. Knowing the basics of the language of course will go a long way, learn as much of it as you can. As long as you can find the solution to new problems, however, you'll be invaluable as an intern and eventually employee. Good luck! I'm sure everyone else and their mother will link to this, but here's a solid tutorial: https://github.com/getify/You-Do...