Beyond the basics: 21 TypeScript features you might not know about

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A comprehensive guide covering 21 advanced TypeScript features including readonly arrays with `as const`, type guards with predicates, exhaustive checking with `never`, template literal types, conditional types with `infer`, mapped type modifiers, key remapping, const type parameters, variadic tuples, and unique symbols for

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#typescript

Oct 23, 2025•17m read time•From dev.to

Table of contents

Introduction 1. Readonly arrays, tuples, and as const assertions 2. keyof typeof for object-as-const enums 3. Labeled tuple elements 4. Indexed access and element type extraction 5. User-defined type guards ( arg is T )6. Exhaustive checking with never 7. Type-only imports and exports ( import type / export type )8. Ambient module declarations for non-code assets 9. The satisfies operator 10. Assertion functions ( asserts and asserts x is T )11. Template literal types for string patterns 12. Distributive conditional types 13. infer to capture types inside conditionals 14. Mapped type modifiers ( +readonly , -? , etc.)15. Key remapping in mapped types ( as )16. Const type parameters 17. Variadic tuple types and spreads 18. The this parameter in functions 19. unique symbol for nominal-like typing 20. Module augmentation and declaration merging 21. Constructor signatures and abstract "newable" types

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