Enums in TypeScript: A Comprehensive Guide

An enum gives names to a set of constants. Instead of scattering magic strings or numbers across your codebase, you define them once and reference them everywhere.

enum Color {
  Red,
  Green,
  Blue
}

By default, Red is 0, Green is 1, Blue is 2. You can assign custom values if you prefer strings or specific numbers.

enum Status {
  Active = "ACTIVE",
  Inactive = "INACTIVE",
  Pending = "PENDING"
}

Using an enum in a function:

function getColorName(color: Color): string {
  switch (color) {
    case Color.Red:
      return 'Red';
    case Color.Green:
      return 'Green';
    case Color.Blue:
      return 'Blue';
  }
}

console.log(getColorName(Color.Red));

The trade-off

Enums are convenient, but they're one of the few TypeScript features that emit runtime code. A numeric enum compiles to a reverse-mapping object. A string enum compiles to a plain object.

If you want zero runtime overhead, use a const enum (values get inlined at compile time) or a union type:

type Color = 'Red' | 'Green' | 'Blue';

Union types don't exist at runtime — they're erased during compilation. But you lose the ability to iterate over values or use reverse mappings.

I use enums when I need runtime access to the values. I use union types when I only need compile-time checking. Pick the one that fits your situation.