Const enum

2 snippets in TypeScript

Also written as as const enum

TSTypeScript

const Enums

syntax

const enum Name {
  Member = value,
}

example

const enum Direction {
  Up = "UP",
  Down = "DOWN",
  Left = "LEFT",
  Right = "RIGHT",
}

const playerDirection = Direction.Up;
// Compiles to: const playerDirection = "UP";
// No Direction object exists at runtime

output

// const enums are completely erased — values are inlined at compile time

Note const enums produce zero runtime JavaScript — member accesses are replaced with literal values. However, they have compatibility issues: they cannot be used with --isolatedModules (Babel, esbuild, SWC), and they do not work across declaration files in some setups. Many teams ban them in favor of plain unions.

Union Types as Enum Alternatives

TS · Enums

syntax

type Name = "value1" | "value2" | "value3";

example

// Instead of enum:
type Theme = "light" | "dark" | "system";

// Object const pattern for when you need both runtime values and types
const THEMES = {
  Light: "light",
  Dark: "dark",
  System: "system",
} as const;

type Theme2 = (typeof THEMES)[keyof typeof THEMES];
// "light" | "dark" | "system"

function applyTheme(theme: Theme2) {
  document.body.dataset.theme = theme;
}

output

// Union types achieve the same result without enum's quirks

Note Many TypeScript teams prefer string literal unions over enums for simplicity, full tree-shaking, and compatibility with --isolatedModules. The 'as const' object pattern gives you both runtime values (for iteration/lookup) and a derived type — the best of both worlds.