The never type represents values that never occur. Here's how to use it effectively.
Understanding never
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Functions That Never Return
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Exhaustive Checking
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Type Narrowing
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Conditional Types
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Impossible States
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Function Overloads
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Generic Constraints
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Error Handling Patterns
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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
Conclusion
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.