Type-level Programming ƒun in TypeScript
summary
Type-level programming in TypeScript shows how to turn URL strings into exact response types and make fetch return Promise<CorrectType> instead of any, using string literal unions, keyof and indexed access types, conditional types and generic type aliases. Examples include a typed fetch mapping URLs to response types, a type-level finite state machine that yields editor autocomplete, boolean-logic gates and Peano-style type numerals with recursive type-level loops. Everything emits zero JavaScript, it improves compile-time errors and IDE suggestions, but it remains brittle across TypeScript version changes.
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chapters (7)
- 0:00The role of types
- 3:57Compilation vs. runtime
- 7:18Refining type safety
- 11:53Introduction to type-level
- 17:12Advanced type mapping
- 25:26Type-level state machines
- 29:52Logic and recursion at types
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