A variable is a named box for a value of a certain type.

Variable declaration is accomplished with let:

let a = 3;
let b1 = 10, b2 = 100, b3 = 1.01;
let c : any;

A constant can be declared with const. A constant needs an initial value and cannot be changed. It is important to mark true constants with const since compilers can make use of that information to produce faster code.

const pi = 3.141592;
const folder = `/data/space-x/content`;

Global constants usually are defined in ALL_CAPS:

const DB_USER = "groucho";
const DB_PORT = 8080;

Variable names

Variables names in Typescript have less constraints than in other languages. In Typescript variable names can contain $ and unicode characters (including emojis!). Except for this, they are usually made from letters (both lowercase and uppercase) and digits (not at the beginning).