When enums add unnecessary runtime code in Typescript

Introduction

Enums in TypeScript create extra code that runs when your program runs. Sometimes, this extra code is not needed and can make your program bigger and slower.

When you want to group related constant values without extra code.

When you only need type checking and not actual values at runtime.

When you want to keep your code small and fast for web apps.

When you prefer using simple objects or union types instead of enums.

Syntax

Typescript

enum Color {
  Red,
  Green,
  Blue
}

This syntax creates an enum named Color with three values.

TypeScript generates JavaScript code to represent this enum at runtime.

Examples

Enum with custom starting number. Values auto-increment.

Typescript

enum Direction {
  Up = 1,
  Down,
  Left,
  Right
}

const enum tells TypeScript to remove enum code at runtime and inline values.

Typescript

const enum Status {
  Active,
  Inactive,
  Pending
}

Using a union of string literals instead of an enum to avoid runtime code.

Typescript

type Status = "Active" | "Inactive" | "Pending";

Sample Program

This program defines an enum and prints the numeric value of Color.Green.

Typescript

enum Color {
  Red,
  Green,
  Blue
}

function printColor(color: Color) {
  console.log(color);
}

printColor(Color.Green);

Important Notes

Regular enums generate JavaScript objects that exist when the program runs.

const enum removes this extra code but only works with TypeScript compilation.

Using union types or simple constants can avoid runtime code and keep programs smaller.

Summary

Enums add extra code that runs with your program.

This extra code can be unnecessary if you only need type checks.

Use const enum or union types to avoid extra runtime code.