JavaScript has three main features that commonly trip up people from other languages. If you understand these three things, you'll be way ahead of the curve:

1) What `this` means in a function context https://developer.mozilla.org/en-US/docs/JavaScript/Referenc...

2) The prototype chain and prototypal inheritance https://developer.mozilla.org/en-US/docs/JavaScript/Introduc...

3) Function closures and variable scoping https://developer.mozilla.org/en-US/docs/JavaScript/Guide/Cl...