Typescript Interview Questions and Answers for 7 years experience

1. What are the key differences between TypeScript and JavaScript?

   • Answer: TypeScript is a superset of JavaScript that adds optional static typing, interfaces, classes, and modules. JavaScript is dynamically typed and interpreted, while TypeScript is statically typed and compiled. TypeScript offers better code maintainability and scalability for larger projects due to its type system, catching errors during development rather than runtime. JavaScript is more widely used and has broader browser compatibility out of the box.

2. Explain the concept of interfaces in TypeScript.

   • Answer: Interfaces define the shape of an object, specifying the types of its properties and methods. They don't provide implementation details; they're purely for defining contracts. Interfaces enhance code readability and maintainability by enforcing type safety. They can be extended and implemented by classes and objects, enabling polymorphism.

3. What are generics in TypeScript and why are they useful?

   • Answer: Generics allow you to write reusable code components that can work with different types without losing type safety. Instead of specifying a concrete type, you use a type parameter (e.g., `T`). This is particularly helpful for functions, classes, and interfaces that operate on collections or data structures where the element type might vary. Generics improve code reusability and type safety.

4. Describe different ways to define types in TypeScript.

   • Answer: TypeScript offers several ways to define types: using primitives (number, string, boolean, etc.), interfaces, type aliases (`type MyType = string;`), enums, tuples, arrays, union types (`string | number`), intersection types (`string & number`), and literal types (`"hello"`).

5. Explain the concept of type guards in TypeScript.

   • Answer: Type guards are functions that refine the type of a variable based on runtime checks. They allow TypeScript's type system to narrow down the possible types of a variable, preventing runtime errors. Common examples include `typeof`, `instanceof`, and custom functions that return a boolean indicating a specific type.

6. What are access modifiers in TypeScript (public, private, protected)?

   • Answer: Access modifiers control the accessibility of class members. `public` members are accessible from anywhere. `private` members are only accessible within the class where they are defined. `protected` members are accessible within the class and its subclasses.

7. How do you handle asynchronous operations in TypeScript using Promises or async/await?

   • Answer: Promises represent the eventual result of an asynchronous operation. Async/await provides a cleaner syntax for working with Promises, making asynchronous code look and behave a bit more like synchronous code. `async` functions always return a Promise, and `await` pauses execution until a Promise resolves.

8. Explain the difference between `let`, `const`, and `var` in TypeScript.

   • Answer: `let` and `const` are block-scoped, meaning they are only accessible within the block of code they are defined in (e.g., inside a function or loop). `var` is function-scoped, meaning it's accessible throughout the entire function. `const` declares a constant variable whose value cannot be reassigned, while `let` declares a variable whose value can be reassigned.

9. What are decorators in TypeScript and how are they used?

   • Answer: Decorators are a way to add metadata to classes, methods, and properties. They're functions that are executed at runtime and can modify the behavior of the decorated element. They are commonly used for dependency injection, logging, and aspect-oriented programming.

10. How do you use namespaces in TypeScript? When are they useful?

    • Answer: Namespaces help organize code into logical units, preventing naming conflicts. They provide a way to group related classes, interfaces, and functions under a single name. Namespaces are less common now with the prevalence of modules, but can still be useful for very large legacy projects or in specific situations where modules are not ideal.

11. Describe your experience with testing TypeScript code. What frameworks have you used?

    • Answer: I have extensive experience testing TypeScript code using Jest, Mocha, and Jasmine. I am familiar with various testing patterns, including unit, integration, and end-to-end testing. I utilize mocking libraries to isolate units of code for testing and ensure high code coverage.

12. Explain your experience with TypeScript in large-scale projects. What challenges have you faced and how did you overcome them?

    • Answer: In large-scale projects, I have successfully used TypeScript to improve code maintainability and scalability. Challenges included managing complex type hierarchies, optimizing build times, and coordinating efforts across a large team. I addressed these by implementing clear coding standards, using build optimization techniques, and employing version control effectively.

13. How do you handle type compatibility issues between different parts of your codebase?

    • Answer: Type compatibility issues are addressed through careful design of interfaces and types, using type guards and assertions strategically, and employing tools like TypeScript's compiler options to control strictness. When necessary, I use type casting carefully but try to refactor code to avoid casting wherever possible.

14. How familiar are you with different build systems for TypeScript? (e.g., Webpack, Parcel, Rollup)

    • Answer: I have experience with Webpack, Parcel, and Rollup, understanding their strengths and weaknesses for different project needs. I can configure these tools to bundle, transpile, and optimize TypeScript code for various environments.

15. Describe your understanding of the TypeScript compiler options and how they affect the build process.

    • Answer: I understand the TypeScript compiler options, such as `target`, `module`, `sourceMap`, `strict`, and others, and how to tailor them for specific build targets and levels of strictness. I know how these options influence the generated JavaScript code and the overall build performance.

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