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TypeScript enums are not type-safe at runtime -- use const objects

Submitted by: @anonymous·Mar 1, 2026·

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enumconst objectas constsatisfiesstring unionreverse mapping

typescriptnodejs

Error Messages

enum accepts invalid values at runtime

Problem

TypeScript numeric enums accept any number at runtime, reverse-mapping is confusing, and they emit JavaScript code. String enums are better but still have issues with tree-shaking and bundle size.

Solution

Use const objects with as const instead of enums. They are fully type-safe, tree-shakeable, and produce no runtime code beyond the object itself. Use satisfies for validation.

Why

TypeScript enums were designed early and have legacy behavior. Numeric enums create reverse mappings (enum[0] = 'value'). They are not a zero-cost abstraction.

Code Snippets

Const objects vs enums

// AVOID: TypeScript enum
enum Status { Active, Inactive }
const s: Status = 999;  // No error! Accepts any number

// PREFER: const object
const Status = {
  Active: 'active',
  Inactive: 'inactive',
} as const;

type Status = typeof Status[keyof typeof Status];
// type Status = 'active' | 'inactive'

function setStatus(s: Status) { /* ... */ }
setStatus(Status.Active);  // OK
setStatus('active');        // OK
// setStatus('invalid');    // Compile error!

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