TypeScript never Type Guide

The never type represents values that never occur. Here's how to use it effectively.

Best Practices#

Use never For:
✓ Exhaustive switch checks
✓ Functions that throw/loop forever
✓ Filtering union types
✓ Representing impossible states

Exhaustive Checking:
✓ Add default case with never
✓ Create assertNever helper
✓ Catch missing cases at compile time
✓ Use discriminated unions

Type Design:
✓ Use never for impossible properties
✓ Filter with conditional types
✓ Validate completeness
✓ Document never in APIs

Avoid:
✗ Assigning to never intentionally
✗ Ignoring never in results
✗ Over-complicating with never
✗ Forgetting exhaustive checks

The never type represents impossibility in TypeScript's type system. Use it for exhaustive checks, functions that don't return, conditional type filtering, and representing impossible states. It's essential for type-safe switch statements and catching missing cases at compile time.

TypeScript never Type Guide

Understanding never#

Functions That Never Return#

Exhaustive Checking#

Type Narrowing#

Conditional Types#

Impossible States#

Function Overloads#

Generic Constraints#

Error Handling Patterns#

Best Practices#

Conclusion#

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