TypeScript

Type-level thinking. Senior+ interviews increasingly ask you to design APIs with types and reason about generics.

Basics #

Topic	Difficulty	Time	Tags	Best Resources
Type basics & inference	🟢	45m	#basics	TS Handbook: everyday types ⭐
Interfaces vs type aliases	🟢	30m	#basics	TS Handbook ⭐
Union & intersection types	🟢	30m	#basics	TS Handbook: unions ⭐
Literal & enum types	🟢	30m	#basics	TS Handbook: enums ⭐
Functions & overloads	🟡	45m	#basics	TS Handbook: functions ⭐
Narrowing & type guards	🟡	45m	#guards	TS Handbook: narrowing ⭐
Discriminated unions	🟡	45m	#patterns #state	TS Handbook ⭐
unknown vs any vs never	🟡	30m	#basics	TS Handbook ⭐

Advanced types #

Topic	Difficulty	Time	Tags	Best Resources
Generics	🟡	1h	#generics	TS Handbook: generics ⭐
Generic constraints & defaults	🟡	45m	#generics	TS Handbook ⭐
Utility types (Partial/Pick/Omit/Record…)	🟡	45m	#utility-types	TS Handbook: utility types ⭐
keyof & typeof	🟡	30m	#type-ops	TS Handbook: keyof ⭐
Indexed access types	🟡	30m	#type-ops	TS Handbook ⭐
Mapped types	🔴	1h	#type-ops	TS Handbook: mapped types ⭐
Conditional types & infer	🔴	1.5h	#type-ops #advanced	TS Handbook: conditional types ⭐
Template literal types	🔴	1h	#type-ops #advanced	TS Handbook ⭐
Variance & assignability	🔴	1h	#advanced	TS Handbook ⭐
Type-level programming	🔴	2h	#advanced	Type Challenges ⭐

Tooling & practice #

Topic	Difficulty	Time	Tags	Best Resources
Declaration files (.d.ts)	🟡	45m	#config	TS Handbook ⭐
Decorators	🟡	45m	#advanced	TS Handbook: decorators ⭐
tsconfig deep dive	🟡	45m	#config	TSConfig reference ⭐
strict mode & flags	🟡	30m	#config	TS Handbook ⭐
Project references & monorepos	🔴	1h	#monorepo #config	TS Handbook ⭐
Typing React components & hooks	🟡	1h	#react	React TS cheatsheet ⭐
Typing async & generics in APIs	🟡	45m	#patterns	TS Handbook ⭐

❓ Rapid-fire TypeScript interview questions #

Real TypeScript interview questions. Answer out loud, then verify above.

1. interface vs type — when to use each?
2. unknown vs any vs never — what's the difference?
3. What are generics and why use them?
4. Explain union vs intersection types.
5. What are type guards and narrowing?
6. What are discriminated unions?
7. Name the common utility types (Partial, Pick, Omit, Record…).
8. What do keyof and typeof do at the type level?
9. What are mapped types?
10. What are conditional types and infer?
11. What are template literal types?
12. What is a declaration file (.d.ts)?
13. What does strict mode turn on?
14. What is the difference between enum and a union of literals?
15. How do you type a React component and its props/hooks?
16. What is structural typing (duck typing)?
17. What is type assertion and when is it dangerous?
18. How do generic constraints (extends) work?
19. What's the difference between readonly and const?
20. How does type inference work and when does it fail?

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Related: 03-javascript · 06-react · 08-architecture

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