TypeScript Enums vs Union Types

Both enums and union types define a set of allowed values. Here's when to use each.

Best Practices#

Union Types:
✓ Prefer for most use cases
✓ Zero runtime overhead
✓ Better tree-shaking
✓ Easy composition

Const Objects:
✓ When you need runtime values
✓ For iteration over values
✓ Namespace organization
✓ Tree-shakeable

String Enums:
✓ Team familiarity
✓ Legacy codebase compatibility
✓ IDE autocomplete preference
✓ Reverse mapping not needed

Avoid:
✗ Numeric enums (type safety issues)
✗ Heterogeneous enums
✗ Computed enum values
✗ Over-engineering simple cases

Prefer union types for most cases—they're simpler, have zero runtime cost, and compose well. Use const objects when you need runtime values and iteration. String enums are acceptable for team preference but avoid numeric enums due to type safety issues.

TypeScript Enums vs Union Types

Basic Enum#

Basic Union Type#

Const Assertions#

Runtime Behavior#

Const Enums#

Type Safety Comparison#

Discriminated Unions#

Bundle Size#

API Design#

Extending and Combining#

Working with Values#

Recommendations#

Best Practices#

Conclusion#

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