Primitive Types

Primitive Types

TypeScript provides type annotations for the three JavaScript primitives you use every day: string, number, and boolean. You write the type after the variable name, separated by a colon.

let username: string = "Alice";
let age: number = 30;
let isActive: boolean = true;

// TypeScript infers these without annotations too:
let city = "Bangalore"; // inferred as string
let score = 100;         // inferred as number

Other primitives include bigint for arbitrarily large integers and symbol for unique identifiers. The special values null and undefined each have their own types. With strictNullChecks enabled, a variable typed string cannot hold null — you must explicitly opt in with a union type.

let id: bigint = 9007199254740993n;
let key: symbol = Symbol("apiKey");

let maybeNull: string | null = null; // OK
let definite: string = null;         // Error with strictNullChecks