Enum vs Type in TypeScript: Pros, Cons, and Best Use Cases

When working with TypeScript, you often need to define a set of specific values that a variable can take. Two popular ways to achieve this are Enums and Union Types.

But which one is better? In this article, we’ll explore Enums and Union Types, their advantages, disadvantages, and real-world use cases.

What is an Enum?

Enums in TypeScript allow you to define a collection of related constants under a single name. Enums are available at runtime and can be numeric or string-based.

Example of an Enum

enum UserRole {
  Admin = "admin",
  Editor = "editor",
  Viewer = "viewer"
}

function getPermissions(role: UserRole) {
  switch (role) {
    case UserRole.Admin:
      return "Full access";
    case UserRole.Editor:
      return "Edit access";
    case UserRole.Viewer:
      return "Read-only access";
    default:
      return "No access";
  }
}

console.log(getPermissions(UserRole.Editor)); // Output: Edit access

Pros of Using Enums ✅

1. Better Readability - Grouping related constants under a single enum name improves code clarity.
2. Auto-completion in IDEs - TypeScript recognizes enum values and provides autocompletion.
3. Runtime Support - Unlike type, enums exist at runtime, making them useful in debugging.

Cons of Using Enums ❌

1. Additional JavaScript Code - Enums generate extra JavaScript code, increasing bundle size.
2. Less Type Safety - Enums allow reverse mapping (UserRole["admin"] === "Admin"), which can lead to unexpected behavior.
3. Performance Overhead - They can introduce unnecessary runtime overhead in large applications.

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What is a Union Type?

A Union Type is a type alias that defines a set of specific string or number values, without generating additional JavaScript code.

Example of a Union Type

type UserRole = "admin" | "editor" | "viewer";

function getPermissions(role: UserRole) {
  switch (role) {
    case "admin":
      return "Full access";
    case "editor":
      return "Edit access";
    case "viewer":
      return "Read-only access";
    default:
      return "No access";
  }
}

console.log(getPermissions("editor")); // Output: Edit access

Pros of Using Union Types ✅

1. Zero Runtime Cost - Since type only exists at compile-time, no extra JavaScript is generated.
2. Better Type Safety - Prevents unwanted reverse mapping behavior.
3. Lightweight and Faster - Works well in performance-critical applications.

Cons of Using Union Types ❌

1. No Runtime Representation - You cannot reference a type at runtime (e.g., UserRole.Editor is invalid).
2. Less Readability in Large Enums - When dealing with many values, Enums are easier to manage.

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When to Use Enum vs Type?

| Feature | Enum | Union Type | | ---------------------- | --------------------- | --------------------------------- | | Runtime Support | ✅ Yes | ❌ No | | IDE Autocompletion | ✅ Yes | ✅ Yes | | Type Safety | ⚠️ Partial | ✅ Strong | | Performance | ❌ Slight Overhead | ✅ Lightweight | | Readability | ✅ Good for large sets | ❌ Harder to manage for large sets |

Best Use Cases

• Use enum when:

  • You need runtime representation (e.g., logging, debugging).
  • You are working with a large set of values that should be grouped under one entity.

• Use type when:

  • You want a lightweight solution with no runtime overhead.
  • You need strict type safety.

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Final Verdict: Which One is Better?

• If you need a simple and efficient solution, use a type.
• If you need runtime behavior, use an enum.

For most cases, union types (type) are preferable because they are more lightweight and safer. However, enums are still useful in specific scenarios.