Like learning any new language, your knowledge can drip away when your focus shifts.

My focus did indeed shift over the past month - from intense language learning (JavaScript!) to interview prep to strictly coding practice.

What I really needed, silly me, was a sweet lil' mixture of coding and concepts.

Reviewing JavaScript basics, most concepts soaked right back in - except for one.

Closures

Originally a mathematical concept, from lambda calculus (did you know that?! me neither!). But for our purposes here, we know a closure to be a behavior of functions.

And only functions.

An object cannot have closure.

Nor does a class have closure.

Only functions.

For closure to be observed, a function must be invoked.

And, it must be invoked in a different branch of the scope chain from where it was originally defined.

Closure Simply Defined

Each reference from an inner function to the variables in an outer scope is called a closure.

Closure's Purpose

A closure gives you access to an outer function’s scope from an inner function.

The closure is a function that remembers the variables from the place where it is defined, regardless of where it is executed later.

Many (and I mean many) other authors claimed to explain closures simply, but I believe Dmitri Pavluti did it best:

Simple Explanation of Closures

Have a different resource or explanation that helped closures "click" for you? Share below - would love to hear more.