50 Essential TypeScript Interview Questions That You Must Prepare

TypeScript has become a fundamental technology in modern web development, bringing strong typing and advanced features to JavaScript. In the field of software engineering, a TypeScript interview requires a deep understanding of its concepts, language features, and best practices. In this article, we will explore the 50 top TypeScript interview questions, spanning different skill levels, to help both freshers and experienced developers prepare effectively.

This Story also Contains

1. Foundational TypeScript Interview Questions
2. Intermediate TypeScript Interview Questions And Answers
3. Java Certification Courses by Top Providers
4. Advanced TypeScript Interview Questions For Experienced Developers
5. Conclusion

TypeScript interview questions cover a wide range of topics, from the basics to more advanced concepts. Here, we have categorised the questions into three levels: Foundational, Intermediate, and Advanced. This structure ensures that you have a comprehensive overview of TypeScript, whether you are just starting or are well-versed in the language. Read more to learn about online Javascript courses.

Foundational TypeScript Interview Questions

Q1. What is TypeScript, and how does it relate to JavaScript?

A. TypeScript is a statically typed superset of JavaScript that compiles to plain JavaScript. It adds optional types, interfaces, and other features to enhance the development experience.

Q2. Explain the benefits of using TypeScript in a project.

A. TypeScript offers an array of compelling benefits. It provides robust type safety, reducing the chances of runtime errors. Additionally, it enhances code organisation, making complex projects more manageable. Improved tooling and early error detection streamline development, while TypeScript's type annotations enhance code readability, promoting collaboration among developers. This is another important type script interview questions asked of the candidates.

Q3. How do you define a variable with a specific type in TypeScript?

A. This is one of the common TypeScript interview questions. To define a variable with a specific type in TypeScript, you employ the syntax: `let variableName: type = value;`, where 'type' specifies the desired data type. This approach ensures that the variable can only store values conforming to the defined type, enhancing code safety and readability.

Q4. Differentiate between null and undefined in TypeScript.

A. Null represents the intentional absence of a value, while undefined signifies a variable that has been declared but has not been assigned a value yet.

Q5. What is type inference in TypeScript?

A. Type inference in TypeScript is the process by which the compiler deduces the data type of a variable without explicit type annotations. It analyses the assigned value during variable declaration and assigns the most appropriate type, enhancing code readability and reducing the need for manual type specifications.

Q6. Explain the concept of interfaces in TypeScript.

A. This is one of the important TypeScript interview questions and answers you should practice. Interfaces define contracts for object structure. They can define properties, methods, and their respective types.

Q7. How does TypeScript handle enums?

A. Enums in TypeScript provide a way to define a set of named constants, which can be more expressive and self-descriptive than raw numeric values. They enhance code readability and maintainability by offering a clear and intuitive representation of specific states or options within your application.

Q8. What is the use of any type in TypeScript?

A. The "any" type in TypeScript serves as a versatile escape hatch from strict type checking. It permits variables to accept values of any type, granting developers flexibility when working with dynamically typed or untyped data, although its overuse can compromise type safety and code maintainability.

Q9. What is the "never" type used for in TypeScript?

A. This type of interview questions on TypeScript are frequently asked. The "never" type is employed as a return type for functions that are intended to never return or always throw errors. It signifies a point in code that should never be reached, aiding in making code more robust and comprehensible.

Q10. Explain the role of generics in TypeScript.

A. Generics empower developers to craft versatile, reusable code components by enabling the parameterization of types within class, interface, and function definitions. They enhance code flexibility and maintainability by accommodating various data types while preserving strong typing principles.

Intermediate TypeScript Interview Questions And Answers

Q11. How can you handle asynchronous operations in TypeScript?

A. Async/await syntax provides a more readable way to work with Promises, making asynchronous code resemble synchronous code. It simplifies error handling through try-catch blocks and enhances code comprehension by allowing developers to write asynchronous operations in a linear, sequential style. This improves maintainability and reduces callback hell, a common issue in callback-based asynchronous JavaScript. This is yet another important type script interview questions asked of the candidates.

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Q12. Describe the differences between classes and interfaces in TypeScript.

A. This is one of the top TypeScript interview questions for freshers and experienced professionals. Classes can have both implementation and constructor logic, while interfaces only define contracts for structure. Classes also support inheritance and access modifiers.

Q13. What is the readonly modifier in TypeScript?

A. The `readonly` modifier in TypeScript serves as a safeguard against unintentional changes to a property or variable after its initial value assignment. Once marked as `readonly`, a property or variable cannot be modified, ensuring data integrity and preventing inadvertent alterations in the codebase.

Q14. How can you achieve type compatibility in TypeScript?

A. In TypeScript, achieving type compatibility relies on structural typing. If two types exhibit identical structure, including properties and methods, they are deemed compatible. This allows for flexibility in function and object assignments, promoting code reusability and flexibility in a statically typed environment.

Q15. Explain the concept of decorators in TypeScript.

A. This is one of the best interview questions on TypeScript. Decorators are used to annotate classes, methods, properties, or parameters and provide metadata that can be used for various purposes, such as logging or dependency injection.

Q16. How do you use namespaces in TypeScript for organising code?

A. In TypeScript, namespaces serve as a structural container to encapsulate code, preventing naming clashes and promoting well-organised codebases. By encapsulating related functions, classes, or interfaces within a namespace, developers can maintain a cleaner and more manageable project structure, enhancing code modularity and collaboration.

Q17. What is the never type in TypeScript?

A. The never type represents values that will never occur. For example, a function that always throws an error has a return type of never.

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Q18. Describe the differences between type assertion and type casting.

A. This type of TypeScript interview questions and answers are important to learn. Type assertion is a way to tell the compiler a specific type, while type casting involves changing the type of a value at runtime, which TypeScript does not support directly.

Q19. How can you use interfaces to define function types?

A. Interfaces can be used to define function types, specifying the parameter types and return type of functions.

Q20. Explain the concept of type guards in TypeScript.

A. Type guards in TypeScript are expressions used within conditional statements to enhance type safety. They enable developers to check and narrow down the possible types of a variable, making it more precise and preventing type-related errors during runtime. This ensures code reliability in dynamic scenarios.

Q21. What is the "tsconfig.json" file in TypeScript, and what is its purpose?

A. The "tsconfig.json" file is a configuration file used in TypeScript projects to specify compiler options, include/exclude files, and other project settings.

Q22. Explain the concept of type alias in TypeScript.

A. A type alias in TypeScript is a user-defined name for a specific type, offering code clarity and manageability. It simplifies complex types and promotes reusability, enhancing code readability and maintainability by providing descriptive labels for intricate type structures.

Q23. What is the "keyof" keyword in TypeScript?

A. "keyof" is a TypeScript keyword utilised to extract keys from object types. This is frequently employed with mapped types to create new types based on the properties of existing objects, facilitating dynamic type manipulations.

Q24. What is the key difference between the "let," "const," and "var" declarations in TypeScript?

A. "let" and "const" are block-scoped declarations introduced in ECMAScript 6 (ES6), while "var" is function-scoped and has different scoping rules.

Q25. What is the purpose of the "strict" flag in TypeScript's compiler options?

A. The "strict" flag in the tsconfig.json file enables a set of strict type-checking options that promote safer and more reliable code. It enforces stringent type rules, such as checking for uninitialized variables and disallowing implicit type conversions, ultimately enhancing code quality and preventing potential bugs.

Q26. Explain the concept of type assertion in TypeScript.

A. Type assertion is a mechanism in TypeScript that empowers developers to explicitly inform the compiler about the data type of a variable, overriding its default inference. This is particularly useful when a developer has better knowledge of the variable's type than what the compiler can deduce automatically, enabling more flexibility in working with different data types.

Q27. Explain the concept of type inference in TypeScript.

A. Type inference in TypeScript is the automatic determination of a variable's type based on its assigned value during initialization. This aids in catching type-related errors early in development, enhancing code reliability.

Q28. What is the "keyof" keyword in TypeScript, and how is it used?

A. The "keyof" keyword in TypeScript is utilised to retrieve the keys or property names of an object type. It is particularly useful for scenarios where you need to create dynamic property access or perform operations based on the keys within an object, enhancing code flexibility and maintainability.

Q29. What is the "as" keyword used for in TypeScript?

A. The "as" keyword in TypeScript is employed for type assertions. It enables developers to explicitly specify the data type of a variable or expression, providing a way to override TypeScript's type inference and convey confidence in the variable's type, ensuring compatibility and type safety.

Q30. Explain the concept of type intersection and type union in TypeScript.

A. Type intersection, denoted by "&", merges multiple types into a single type containing all the combined properties. Type union, indicated by "|", permits a value to belong to one of several specified types, providing flexibility in variable assignments and function parameters.

Advanced TypeScript Interview Questions For Experienced Developers

Q31. What are conditional types in TypeScript?

A. Conditional types allow you to create types that depend on other types, enabling more complex type manipulations.

Q32. What are the benefits of using TypeScript with React?

A. This is one of the advanced TypeScript interview questions for experienced individuals. Integrating TypeScript with React yields numerous advantages, including improved code quality through static typing, superior tooling support, enhanced auto-completion, and elevated maintainability, particularly in sizable codebases.

Q33. Describe the concept of mapped types in TypeScript.

A. Mapped types in TypeScript are a powerful feature that allows you to manipulate and transform properties of one type to create new types. They provide a concise way to modify existing types by applying a function to each property, making it a valuable tool for creating variations of data structures while maintaining type safety and code readability.

Q34. How do you create and use module declarations in TypeScript?

A. This is one of the TypeScript interview questions you must know. Module declarations are used to tell TypeScript about the shape of external modules or libraries that are written in JavaScript.

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Q35. Explain the differences between ambient declarations and regular TypeScript declarations.

A. Ambient declarations in TypeScript are used to define types and interfaces for external libraries or modules that exist in the runtime environment but may not have TypeScript definitions within the project. They provide a way to interact with non-TypeScript code, enabling type-checking and code completion while working with external dependencies.

Q36. What are namespaces and when should you use them in TypeScript?

A. Namespaces in TypeScript offer a method to group related code within a distinct container, preventing naming clashes and enhancing code organisation. However, they have become less popular in favour of modern module systems like ES6 modules, which offer a more efficient and scalable approach to structuring code in TypeScript projects.

Q37. How can you handle union types and intersection types in TypeScript?

A. This type of TypeScript interview questions and answers are very common. Union types allow a variable to hold values of multiple types, while intersection types represent a type that has the characteristics of all the types in the intersection.

Q38. Explain the concept of declaration merging in TypeScript.

A. Declaration merging in TypeScript is a feature that enables you to combine multiple declarations of the same entity, such as interfaces or types, into a single unified definition. This simplifies code organisation by allowing you to build complex types incrementally, enhancing readability and maintainability.

Q39. What is the purpose of the "as" keyword in TypeScript?

A. The "as" keyword functions as a type assertion in TypeScript, enabling developers to explicitly specify a value's type, overriding the default type inference. It is crucial for handling situations where type precision is essential.

Q40. What are some advanced techniques to achieve stricter type-checking in TypeScript?

A. This is one of the advanced TypeScript interview questions you must practice. Achieving stricter type checking in TypeScript involves various advanced strategies. Firstly, enabling strict null checks ensures variables are properly initialised. Secondly, avoiding the "any" type promotes strong typing. Lastly, using advanced type features such as mapped types and conditional types enhances code accuracy and type safety. These techniques collectively contribute to a robust TypeScript codebase.

Q41. How can you achieve runtime type checking in TypeScript?

A. Runtime type checking can be implemented using third-party libraries like "prop-types" in React. These libraries examine types during development and provide runtime warnings if type inconsistencies are detected, bolstering code reliability.

Q42. What is the purpose of the "declaration" option in TypeScript's tsconfig.json file?

A. The "declaration" option, when set to true in the tsconfig.json file, generates corresponding ".d.ts" declaration files alongside your compiled JavaScript. These declaration files are crucial for providing type information to developers using your TypeScript code as a library or module, enhancing code understanding and compatibility.

Q43. What is a type predicate in TypeScript, and why is it useful?

A. A type predicate is a user-defined function that narrows the type of a value within a conditional block, enhancing type safety.

Q44. How can you use conditional types to create flexible and reusable type definitions?

A. Conditional types allow you to define types that depend on other types, enabling advanced type manipulation and creating flexible and reusable type definitions.

Q45. What are type guards, and how do they improve code reliability in TypeScript?

A. Type guards are functions or expressions in TypeScript that assist the compiler in determining and refining the type of a variable or value within a conditional block. By providing these guards, developers enhance code reliability by ensuring that the correct type-specific operations are applied, reducing the likelihood of unexpected runtime errors.

Q46. Explain the purpose of the "unknown" type in TypeScript.

A. The "unknown" type represents a value of an unknown type, providing type safety while allowing flexibility in type checking. It is a more restrictive alternative to the "any" type, ensuring that developers make explicit type assertions before using values of this type. This enhances code safety and maintainability.

Q47. What is the purpose of the "never" type in TypeScript, and when is it commonly used?

A. The "never" type represents values that will never occur, often used for functions that always throw errors or in exhaustive switch cases.

Q48. What is the role of TypeScript's "tsconfig.json" file in a project?

A. The "tsconfig.json" file configures TypeScript compiler options for a project, including compilation settings, file inclusion/exclusion rules, and project-specific configurations. It fosters consistency and compatibility within the codebase by ensuring uniform compilation parameters.

Q49. What is the "infer" keyword in TypeScript's conditional types, and how does it work?

A. The "infer" keyword is used to extract and infer types within conditional type expressions, enabling complex type manipulations.

Q50. Explain the concept of nominal typing and how it differs from structural typing in TypeScript.

A. Nominal typing relies on the name of a type for compatibility, while structural typing is based on the shape of a type. TypeScript primarily uses structural typing, but nominal typing can be achieved using unique symbols or tagged unions.

Conclusion

By reviewing these 50 top TypeScript interview questions and answers, you will be ready for various TypeScript challenges in interviews. Remember, blending your technical understanding with clear communication boosts your success odds. As TypeScript gains importance in development, understanding it becomes valuable, and this article lays a strong groundwork for that journey.