Typescript Interview Questions and Answers by Scholarhat

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1. Typescript Interview Questions and Answers by Scholarhat To prepare for technical interviews, many developers rely on trusted resources like the TypeScript Interview Questions and Answers by ScholarHat, which cover everything from basic syntax to advanced TypeScript concepts in a concise and practical format.
2. Why TypeScript? • Type Safety: Catches errors at compile-time, preventing runtime crashes. • Scalability: Ideal for large, complex projects with maintainable codebases. • Improved Tooling: Powerful IDE features like autocompletion and refactoring. • Readability: Clear, self-documenting code using explicit types. • Modern Features: Fully supports the latest ECMAScript standards.
3. Core Concepts: Types and Interfaces Primitive Types string, number, boolean, null, undefined, symbol, bigint Any vs Unknown any: skips type checks; unknown: safer, requires explicit casting Interfaces & Aliases Define object shapes and create custom type names Void & Never Void for no return; never for unreachable code
4. Core Concepts: Classes and Enums • Classes: Blueprints with inheritance and access modifiers (public, private, protected). • Abstract Classes: Cannot instantiate directly, define required methods. • Enums: Named constant sets to improve code clarity. • Generics: Create reusable, type-safe components. • Modules: Organize code logically across files.
5. Advanced Concepts: Generics Type Parameters Functions and classes that work with any type while maintaining safety. Constraints Limit generics with 'extends' for more precise typing. Common Use Cases Examples: Array<string>, Promise<number>, Map<K, V>.
6. Advanced Concepts: Utility Types Partial<T> Makes all properties optional. Readonly<T> Makes properties immutable. Pick<T, K> Selects subset of properties. Omit<T, K> Removes specified properties. Exclude<T, U> Excludes union members assignable to U. Conditional Types Transforms types based on conditions (e.g. T extends U ? X : Y).
7. TypeScript vs. JavaScript Static vs Dynamic TS checks types at compile time; JS checks during runtime. Compilation TS compiles to JS, which browsers execute directly. Error Detection TS catches errors earlier, reducing runtime bugs. Tooling Support TS provides stronger IDE tools and refactoring. Scalability TS handles large apps; JS fits smaller scripts better.
8. Modules and Namespaces • Modules: Use import/export to keep code organized with private scope. • Namespaces: Legacy internal grouping before ES modules became standard. • Declaration Files (.d.ts): Provide type info for JS libraries and tools. • Triple-Slash Directives: Older way to reference declaration files.
9. Decorators and Type Guards Decorators Add metadata to classes, methods, or properties (experimental feature). Type Guards Runtime checks narrow variable types using typeof, instanceof, or custom checks. Intersection & Union Combine types (&) or allow multiple possible types (|). Type Assertion Cast variables to specific types without runtime overhead.
10. Best Practices & Conclusion • Enable Strict Mode to catch common errors and improve safety. • Use consistent linting with ESLint to enforce code quality. • Favor immutability using Readonly types for reliability. • Design explicit, clear interfaces to define data contracts. • Leverage advanced tooling for better productivity. • Commit to continuous learning as TypeScript evolves rapidly.