Literal Types

A Literal Type is a single element set from a collective type, it defines a very exact value that is a JavaScript primitive.

Literal Types in TypeScript are numbers, strings, and booleans.

Example of literals:

const a = 'a'; // String literal type
const b = 1; // Numeric literal type
const c = true; // Boolean literal type

String, Numeric, and Boolean Literal Types are used in the union, type guard, and type aliases. In the following example you can see a type alias union, O can be the only value specified and not any other string:

type O = 'a' | 'b' | 'c';