First off, why are closures important to know? The best answer to this so far in my eyes is because it's a common interview question.

The Basics: Lexical Scope

Let's start with what we already know and build up from there.

JS Functions have access to:

1. variables outside of the function
2. variables on the same level of the function

For example take the following code:

let outside = "fishbowl";

const checkScope = () => {
    let inside = "goldfish";
    console.log(outside);
    console.log(inside);
};

checkScope(); //logs fishbowl and goldfish

JavaScript functions have access to variable in the environment of where it was defined, not where it is called.

Closures

? Is it the same as private variables in classes in java? ? You don't want to run a function that ends up affecting all the other private variables of another type