Literal Types & Enums

8 min read

Literal Types & Enums

Literal types

A literal type constrains a variable to an exact value rather than a broad primitive. String, number, and boolean literals are all supported.

type Direction = "north" | "south" | "east" | "west";
type DiceRoll = 1 | 2 | 3 | 4 | 5 | 6;
type Toggle = true | false; // equivalent to boolean

function move(dir: Direction) {
  console.log("Moving:", dir);
}

move("north"); // OK
move("up");    // Error — not in the union

Enums

Enums declare a set of named constants. Unlike literal type unions, numeric enums produce actual JavaScript output. Const enums are fully erased at compile time.

// Numeric enum (compiled to an object)
enum Role {
  Student,   // 0
  Mentor,    // 1
  Admin      // 2
}

// String enum (safer for serialization)
enum Color {
  Red = "RED",
  Green = "GREEN",
  Blue = "BLUE"
}

// Const enum (inlined, no runtime object)
const enum HttpStatus {
  OK = 200,
  NotFound = 404,
  InternalError = 500
}

const status: HttpStatus = HttpStatus.OK; // compiled to: const status = 200

Many TypeScript practitioners prefer literal union types ("red" | "green" | "blue") over enums because they are simpler, have no runtime footprint, and serialize naturally. Use enums when you need auto-incremented numbers or need to iterate over values.

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