Literal Types

Syntax

let value: "specific-string" | 42 | true;

Examples

type Direction = "up" | "down" | "left" | "right";
type DiceRoll = 1 | 2 | 3 | 4 | 5 | 6;

function move(direction: Direction) {
  console.log(`Moving ${direction}`);
}

move("up");     // OK
// move("north"); // Error - not one of the allowed literals

let a = "hello";       // inferred as: string (widened)
const b = "hello";     // inferred as: "hello" (literal, since const cannot be reassigned)

let config = {
  mode: "production"
} as const;
// config.mode is typed as the literal "production", not string
// config.mode = "development"; // Error - as const also makes properties readonly

Best practices

• Use literal type unions instead of a general string/number type when a value only has a small, known set of valid options - it catches typos at compile time
• Use as const on object/array literals to lock in their most specific literal types, especially useful for configuration objects
• Combine literal types with discriminated unions for exhaustive, type-safe handling of different variant shapes
• Prefer literal unions over TypeScript enums for simple cases - they compile to nothing extra and integrate more naturally with plain JavaScript

At a glance

Purpose

Static types for JavaScript

File extension

.ts · .tsx

Runs in

Compiled to JavaScript

Usually used with

JavaScript and its ecosystem

Specifications & further reading

• TypeScript Handbook

Related TypeScript documentation