Typescript Interview Questions and Answers for internship

1. What is TypeScript and why is it used?

   • Answer: TypeScript is a superset of JavaScript that adds optional static typing. It's used to improve code maintainability, readability, and scalability in large projects. The static typing allows for early error detection during development, reducing runtime errors and improving developer productivity.

2. 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 within the entire function it's defined in. `const` declares a constant whose value cannot be reassigned after initialization. `let` declares a variable whose value can be reassigned. `var` is generally discouraged in modern TypeScript due to its potential for unexpected behavior.

3. What are interfaces in TypeScript and how are they used?

   • Answer: Interfaces define the shape of an object, specifying the properties and their types. They are used to enforce type consistency and improve code readability. Interfaces don't provide implementations; they only define contracts.

4. Explain type aliases in TypeScript. How do they differ from interfaces?

   • Answer: Type aliases create a new name for an existing type. They are similar to interfaces in that they define types, but they can also alias primitive types, unions, and tuples, which interfaces cannot. Interfaces, on the other hand, can extend other interfaces, something type aliases cannot do.

5. 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. This is achieved by using type parameters (e.g., ``). Generics prevent type errors when working with different data types and enhance code reusability.

6. Explain the concept of type inference in TypeScript.

   • Answer: Type inference is TypeScript's ability to automatically deduce the type of a variable based on its value or usage. This reduces the need for explicit type annotations in many cases, making code cleaner and more concise.

7. What are union types and intersection types in TypeScript? Provide examples.

   • Answer: Union types (`|`) allow a variable to hold values of multiple types. Example: `let value: string | number = "hello"; value = 123;`. Intersection types (`&`) combine multiple types into a single type that must satisfy all types. Example: `interface Person { name: string; } interface Employee { id: number; } let personEmployee: Person & Employee = { name: "John", id: 123 };`

8. Explain optional properties in TypeScript interfaces.

   • Answer: Optional properties in interfaces are declared using a question mark (`?`) after the property name. Example: `interface User { name: string; age?: number; }`. This means that the `age` property is not required when creating objects that conform to the `User` interface.

9. How do you handle null and undefined values in TypeScript?

   • Answer: You can use optional properties (`?`), union types (e.g., `string | null | undefined`), or the non-null assertion operator (`!`) to handle null and undefined values. The `typeof` operator can also be used to check if a variable is null or undefined. The strictNullChecks compiler option enhances null and undefined checking.

10. What are type guards in TypeScript? Give an example.

    • Answer: Type guards are functions that narrow down the type of a variable at runtime. They help TypeScript understand the precise type of a variable in conditional statements. Example: `function isString(value: any): value is string { return typeof value === 'string'; }`

11. Describe your experience working with TypeScript in a team environment.

    • Answer: [Describe your experience, highlighting collaboration, code reviews, and adherence to coding standards. If you lack team experience, focus on your understanding of collaboration and best practices.]

12. What are some common challenges you've faced while using TypeScript and how did you overcome them?

    • Answer: [Describe specific challenges, such as type errors, complex generics, or integrating with JavaScript libraries. Explain your problem-solving approach and any resources you used to resolve them.]

13. How do you stay up-to-date with the latest developments in TypeScript?

    • Answer: [Mention resources such as the official TypeScript website, blog, documentation, newsletters, and relevant online communities.]

14. What are your favorite TypeScript features and why?

    • Answer: [List your preferred features, such as interfaces, generics, type inference, or type guards, and explain why you find them useful and efficient.]

15. How would you approach debugging a TypeScript application?

    • Answer: [Explain your debugging strategy, encompassing the use of a debugger, console logging, error messages, and testing frameworks.]

16. Explain your understanding of TypeScript's module system.

    • Answer: [Discuss the common module systems used in TypeScript, such as CommonJS and ES modules, and their advantages and disadvantages.]

17. How familiar are you with testing in TypeScript? What frameworks have you used?

    • Answer: [Explain your knowledge of testing methodologies like unit, integration, and end-to-end testing. Mention any relevant frameworks such as Jest, Mocha, or Jasmine.]

18. What are decorators in TypeScript and how can they be used?

    • Answer: [Explain the concept of decorators and their applications in modifying class members, methods, and properties.]

19. How do you handle asynchronous operations in TypeScript?

    • Answer: [Discuss the use of `async`/`await` and promises in handling asynchronous operations, along with error handling techniques.]

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