Day 39 of 100: Enums vs Literal Types — When Each Wins

Day 39 of 100 — 100 Days of Playwright with TypeScript Challenge. Phase: TypeScript. JavaScript (Days 1-33) → TypeScript (Days 34-63) → Playwright (Days 64-96) → AI Framework Capstone (Days 97-100).

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Enums group related constants. Literal unions often do it better. Know both; choose deliberately.

Enum Syntax

enum Env {
  Local = 'http://localhost:3000',
  Staging = 'https://staging.example.com',
  Prod = 'https://example.com',
}

const target: Env = Env.Staging;

enum HttpStatus { OK = 200, Created = 201, NotFound = 404 }
HttpStatus.Created;   // 201

Literal Union Alternative

type Browser = 'chromium' | 'firefox' | 'webkit';
const b: Browser = 'firefox';

// const-object pattern — enum ergonomics, zero runtime cost:
const ENVS = {
  local: 'http://localhost:3000',
  staging: 'https://staging.example.com',
} as const;
type EnvKey = keyof typeof ENVS;   // 'local' | 'staging'

Decision Table

• String literal unions: default choice — zero runtime code, perfect inference
• Enums: when you need a runtime value map (env → URL) referenced by name
• as const objects: best of both — values + derived types
• Avoid numeric auto-enums — opaque values in failure logs

Tomorrow (Day 40): Typing functions — params, returns, async signatures.