TypeScript Interview Questions and Answers 2026 - Top 10 Typed JavaScript Questions
TypeScript Interview Questions and Answers 2026 - Top 10 Typed JavaScript Questions
03-21-2026, 09:48 AM
Keywords: TypeScript interview questions 2026, typed JavaScript interview, TypeScript generics, TypeScript vs JavaScript, frontend TypeScript interview
1. What is TypeScript and how does it differ from JavaScript?
TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. It adds static type checking, interfaces, generics, enums, and decorators. TypeScript catches errors at compile time rather than runtime, improving code quality and developer experience with better IDE support.
2. Explain TypeScript's type system and basic types.
Basic types include string, number, boolean, array, tuple, enum, any, unknown, void, null, undefined, and never. Union types (A | B) allow multiple types. Intersection types (A & B) combine types. Type aliases and interfaces define custom types. Literal types restrict to specific values.
3. What are generics in TypeScript?
Generics create reusable components that work with multiple types while maintaining type safety. Use angle brackets: function identity<T>(arg: T): T. Generic constraints limit types with extends keyword. Generic interfaces and classes create flexible data structures. Built-in generics include Array<T>, Promise<T>.
4. Explain the difference between interface and type alias.
Interfaces are extendable with extends keyword and support declaration merging. Type aliases use = syntax and support union, intersection, and mapped types. Interfaces are preferred for object shapes and class contracts. Type aliases are preferred for unions, primitives, and utility types.
5. What are utility types in TypeScript?
Built-in utility types transform existing types. Partial<T> makes all properties optional. Required<T> makes all required. Readonly<T> prevents mutations. Pick<T,K> selects specific properties. Omit<T,K> excludes properties. Record<K,T> creates key-value types. ReturnType<T> extracts function return type.
6. Explain type guards and narrowing.
Type guards narrow types within conditional blocks. typeof for primitives, instanceof for classes, in for property checking, and custom type predicates (is keyword). Discriminated unions use a common literal property for narrowing. Exhaustive checks use never type.
7. What are mapped types and conditional types?
Mapped types transform properties: { [K in keyof T]: newType }. Conditional types use ternary syntax: T extends U ? X : Y. infer keyword extracts types within conditions. These enable powerful type transformations and are the foundation of many utility types.
8. Explain decorators in TypeScript.
Decorators are special declarations that modify classes, methods, properties, or parameters. They use @expression syntax. Common in Angular and NestJS. Types include class decorators, method decorators, property decorators, and parameter decorators. Enable metadata-driven programming.
9. What is the difference between any, unknown, and never?
any disables type checking entirely (avoid when possible). unknown is the type-safe counterpart requiring type narrowing before use. never represents values that never occur (unreachable code, exhaustive checks). Prefer unknown over any for type safety.
10. How do you configure and optimize a TypeScript project?
tsconfig.json configures compilation options. Key settings include strict mode, target ES version, module system, paths for aliases, and declaration files. Use project references for monorepos. Enable incremental compilation for faster builds. Use skipLibCheck for performance.
Conclusion: TypeScript is essential for modern web development in 2026. Master generics, utility types, type narrowing, and advanced type system features to ace your interviews.
Tags: #TypeScript #InterviewQuestions #JavaScript #Frontend #Generics #WebDevelopment #Angular #TypeScript2026
TypeScript is the standard for modern JavaScript development in 2026 adopted by Angular, Next.js, and most enterprise teams at Microsoft, Google, and Airbnb. Whether you are applying for a Frontend Developer, Full-Stack Engineer, TypeScript Developer, or React Developer role, these top 10 TypeScript interview questions will help you prepare.
Keywords: TypeScript interview questions 2026, typed JavaScript interview, TypeScript generics, TypeScript vs JavaScript, frontend TypeScript interview
1. What is TypeScript and how does it differ from JavaScript?
TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. It adds static type checking, interfaces, generics, enums, and decorators. TypeScript catches errors at compile time rather than runtime, improving code quality and developer experience with better IDE support.
2. Explain TypeScript's type system and basic types.
Basic types include string, number, boolean, array, tuple, enum, any, unknown, void, null, undefined, and never. Union types (A | B) allow multiple types. Intersection types (A & B) combine types. Type aliases and interfaces define custom types. Literal types restrict to specific values.
3. What are generics in TypeScript?
Generics create reusable components that work with multiple types while maintaining type safety. Use angle brackets: function identity<T>(arg: T): T. Generic constraints limit types with extends keyword. Generic interfaces and classes create flexible data structures. Built-in generics include Array<T>, Promise<T>.
4. Explain the difference between interface and type alias.
Interfaces are extendable with extends keyword and support declaration merging. Type aliases use = syntax and support union, intersection, and mapped types. Interfaces are preferred for object shapes and class contracts. Type aliases are preferred for unions, primitives, and utility types.
5. What are utility types in TypeScript?
Built-in utility types transform existing types. Partial<T> makes all properties optional. Required<T> makes all required. Readonly<T> prevents mutations. Pick<T,K> selects specific properties. Omit<T,K> excludes properties. Record<K,T> creates key-value types. ReturnType<T> extracts function return type.
6. Explain type guards and narrowing.
Type guards narrow types within conditional blocks. typeof for primitives, instanceof for classes, in for property checking, and custom type predicates (is keyword). Discriminated unions use a common literal property for narrowing. Exhaustive checks use never type.
7. What are mapped types and conditional types?
Mapped types transform properties: { [K in keyof T]: newType }. Conditional types use ternary syntax: T extends U ? X : Y. infer keyword extracts types within conditions. These enable powerful type transformations and are the foundation of many utility types.
8. Explain decorators in TypeScript.
Decorators are special declarations that modify classes, methods, properties, or parameters. They use @expression syntax. Common in Angular and NestJS. Types include class decorators, method decorators, property decorators, and parameter decorators. Enable metadata-driven programming.
9. What is the difference between any, unknown, and never?
any disables type checking entirely (avoid when possible). unknown is the type-safe counterpart requiring type narrowing before use. never represents values that never occur (unreachable code, exhaustive checks). Prefer unknown over any for type safety.
10. How do you configure and optimize a TypeScript project?
tsconfig.json configures compilation options. Key settings include strict mode, target ES version, module system, paths for aliases, and declaration files. Use project references for monorepos. Enable incremental compilation for faster builds. Use skipLibCheck for performance.
Conclusion: TypeScript is essential for modern web development in 2026. Master generics, utility types, type narrowing, and advanced type system features to ace your interviews.
Tags: #TypeScript #InterviewQuestions #JavaScript #Frontend #Generics #WebDevelopment #Angular #TypeScript2026
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