Nowadays JavaScript has three different keywords to declare a variable — var, let and, const. Each has its own properties and particularities. Let’s start by making a simple comparison table ...

JavaScript variables hold a wide variety of information and can be used with virtually any data type. Here's how to use variables to store numbers, text strings, objects, and more.

OK, I get the part about letting functions directly access memory without allowing them to change things (good if you're working huge-ass arrays!), but what else is it used for?