Answer 1

There are different types of variables in any language and I think (I'm not sure) all languages share the same types of variables. So if you know them in any language, it is already enough.

And to declare variables in JavaScript, you should use: var or let or const.

With "const" keyword you cannot modify that variables.
With let and var, you can do anything.
Differences between var and let 👇👇

https://stackoverflow.com/questions/762011/whats-the-difference-between-using-let-and-var

https://www.google.com/amp/s/www.geeksforgeeks.org/difference-between-var-and-let-in-javascript/amp/