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56 TypeScript interview questions to ask software developers

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TypeScript plays a large role in web development and has become a popular programming language for web developers and programmers. As an open-source superset of JavaScript, TypeScript is useful for a range of large-scale projects. However, it can be challenging for employees to use if they don’t have the right skills. 

Since technology is always improving, engineering managers frequently advertise jobs for computer professionals.

To hire the best talent, first create an effective job description – such as a TypeScript developer job description. Once you have applicants, send each of them a TypeScript coding test to determine whether they have the necessary skills and experience. Afterward, you can ask engaging and relevant questions in an interview. 

If you can’t find the right questions, look at our 56 TypeScript interview questions and answers below to hire talented TypeScript professionals for your team.

20 beginner TypeScript interview questions to use in job interviews

Here are some TypeScript interview questions for beginners with basic programming skills and knowledge of the TypeScript language. 

1. Explain what TypeScript is and how it works.

2. What are arrays in TypeScript?

3. Give me some benefits of using TypeScript.

4. Are there any downsides to using this programming language?

5. What are the differences between TypeScript and JavaScript?

6. List some of TypeScript’s features.

7. What are loop statements? 

8. How do you convert a string to a number? 

9. Do you know what contextual typing means?

10. What is JSX? 

11. What are the import and export keywords in TypeScript? 

12. Define what static typing means.

13. How do you create objects in TypeScript?

14. How do you declare a variable in TypeScript? 

15. Name a few built-in data types in TypeScript.

16. Explain what modules are in this program. 

17. Does TypeScript support function overloading?

18. How do you compile TypeScript files?

19. What are interfaces in TypeScript? 

20. What is the difference between internal modules and external modules?

5 beginner TypeScript interview questions and answers 

Check out these beginner TypeScript interview questions and answers when comparing your candidates’ responses after the interview.

Five beginner TypeScript interview questions

1. Explain what TypeScript is and how it works. 

TypeScript is a programming language that builds on JavaScript, which is another scripting language. Many developers and programmers use this object-oriented language to develop large applications.

Candidates should also know how it works, even if they’re beginners. TypeScript adds enhanced syntax on top of JavaScript to enable developers to include static typing and other additional features. 

Interviewees may also explain that TypeScript is becoming more popular. The number of developers actively using TypeScript almost tripled between 2017 and 2022. This programming language is high in popularity rankings thanks to its various features and unique components that support web development trends. 

You can send candidates a JavaScript coding test to see how much they know about the base programming language.

2. What are the differences between TypeScript and JavaScript?

The ideal candidate should know the difference between these popular programming languages. Although both are mainly used for web development, TypeScript is built on top of JavaScript and adds some additional features, including static typing. 

Here is a table with the key distinctions between JavaScript and TypeScript: 

TypeScript

JavaScript

Adds static typing; Supports modules; Supports type annotations; Suited for large-scale web apps

Only offers dynamic typing; No module support; Doesn’t support type annotations; Service-side language suited for smaller web applications

3. List some of TypeScript’s features. 

TypeScript contains quite a few prominent features that candidates should know about. Their responses will show whether they have enough experience with this programming language. Strong candidates should name each feature and explain how it benefits web projects. 

Here are some of TypeScript’s important features:

  • Cross-platform: Developers can use TypeScript to build applications on a wide range of operating systems, like Windows, MacOS, and Linux.

  • Object-oriented: TypeScript includes interfaces, modules, and classes for designing object-based code and server development. 

  • Static type-checking: Programmers can find coding errors more easily with TypeScript’s static typing and type-checking features. 

  • Optional static typing: Developers can also use optional static typing instead of JavaScript’s dynamic typing.

  • DOM manipulation: This feature manipulates the document object model (DOM) to add or remove specific elements in the web project.

  • ES6 features: TypeScript uses most features from ECMAScript 2015 (ES 6, 7), including arrow functions, interfaces, and classes. 

4. How do you create objects in TypeScript?

Objects in TypeScript are instances that contain a set of key-value pairs that represent properties and methods. 

You can create these objects by following a few methods:

  • Use the object literal notation (which requires curly brackets)

  • Define the objects with constructors

  • Use the Object.create() method

Consider sending candidates a Numerical Reasoning test to evaluate their ability to interpret numbers and understand coding patterns. This knowledge is essential for developer roles that require good numerical skills. 

5. How do you declare a variable in TypeScript?

A variable is a named location that stores data and values. It is a container for a value in the code. One way to declare a variable in TypeScript is by using the var keyword followed by the variable name, a colon, the variable type, the “=” sign, and the variable’s value. Below is an example of how to declare a string variable:

var message: string = “Hello, World!”;

This question will encourage candidates to show their programming skills. Even beginners should understand what objects and variables are in TypeScript. 

18 intermediate TypeScript interview questions to assess applicants’ skills

Use these intermediate TypeScript interview questions for candidates who have some experience working with this programming language.

1. What is an anonymous function in TypeScript?

2. Explain what decorators are. 

3. What are mixins in TypeScript?

4. What is a namespace? How do you declare it?

5. Can you combine multiple .ts files into a single .js file?

6. What is a scope variable?

7. Tell me how to debug a TypeScript file. 

8. What are the steps to include a type definition file in TypeScript?

9. What is the default parameters function?

10. Explain what the tsconfig.json file is. 

11. When do you use ambient declarations in TypeScript? 

12. What are distributive conditional types?

13. When should you use the unknown type?

14. What is the difference between union and intersection types?

15. How do you inherit a class in TypeScript?

16. Tell me what compilation context means. 

17. What is an enum in TypeScript?

18. What do you know about the as keyword in TypeScript?

5 intermediate TypeScript interview questions and answers

Refer to these intermediate TypeScript interview questions and answers when reviewing your candidates’ responses after the interview. 

Five intermediate TypeScript interview questions

1. What is a namespace? How do you declare it?

A namespace, also referred to as an internal module, is a container for variables, functions, classes, and interfaces. Developers use them to help organize and manage their code. 

To declare a namespace, developers must use the namespace keyword followed by a name. Then, include any interfaces or classes in the brackets. Here is an example of how to declare a namespace in TypeScript:

namespace ExampleNamespace {

export var exampleVariable = 1;

export function exampleFunction(): void {

// Function code

}

export class ExampleClass {

// Class code

}

export interface ExampleInterface {

// Interface code

}

}

Candidates should know the importance of clean code when developing large-scale projects in TypeScript. Clean code is essential when declaring namespaces and creating classes or functions.

2. Tell me how to debug a TypeScript file.

Debugging a TypeScript file may be challenging, but candidates with the right experience should know how to do it. To achieve this, programmers should:

  1. Use a .js source map file to start the debugging process

  2. Compile a .ts file with the source flag to develop a source map file in TypeScript 

  3.  Use Visual Studio’s built-in feature to debug files 

Use a TypeScript debugging test to determine whether your candidates can find and resolve bugs in code. Or you can give them our Problem Solving test to see how they handle complex issues in the workplace. 

Research has found that more than 60% of employers want to see evidence of problem-solving skills, so it’s important to use practical skills assessments. 

3. What are distributive conditional types?

Conditional types become distributive conditional types when applied to a union type. They distribute a conditional check over each member of that union. This enables developers to indicate relationships between inputs and outputs based on specific conditions.

4. Explain what decorators are in TypeScript. 

Decorators are an experimental TypeScript feature that enables developers to add additional functionality to properties, methods, parameters, and classes. In this way, they can enhance and add to the behavior of existing code. 

5. What do you know about the as keyword in TypeScript?

The as keyword is used for type assertions in TypeScript. Developers use this feature to override the compiler’s default type inference and explicitly specify a value’s type. 

Candidates with JavaScript development experience will know more about syntax and its complexities. For example, they might explain how as tells the compiler to change the type of specific objects in TypeScript. 

18 advanced TypeScript interview questions for experienced developers

Below are advanced TypeScript interview questions that are suited to experienced computer professionals like web developers and programmers.

1. How do you compile TypeScript with Visual Studio Code?

2. Name some recent advancements in TypeScript. 

3. Tell me more about the awaited type and Promise improvements. 

4. What is type assertion? Give a few examples.

5. What are the rules for declaring rest parameters?

6. How do you call the base class constructor from a child class in TypeScript?

7. Explain how optional chaining works. 

8. What is method overriding in TypeScript?

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

10. List a few rules of private fields in TypeScript.

11. How do you make all properties of an interface optional?

12. What is the difference between type inference and contextual typing?

13. How would you choose between never, unknown, and any in TypeScript?

14. What features does TypeScript offer to help make reusable components?

15. Which TypeScript features would be suitable for a full-stack developer?

16. What are generics in TypeScript?

17. What are arrow/lambda functions in TypeScript?

18. What is the difference between a tuple and an array?

5 advanced TypeScript interview questions and answers 

Check out these advanced interview questions and answers to determine which of your candidates know the most about TypeScript. 

Five advanced TypeScript interview questions

1. What are the rules for declaring rest parameters?

A rest parameter accepts zero or more arguments as an array. Developers need to follow specific rules for declaring rest parameters in TypeScript to avoid code errors and syntax issues. 

Here are some rules for rest parameters: 

  • Only one rest parameter can operate in a function

  • The rest parameter must be declared as an array type

  • The rest parameter needs to be placed last in the parameter list 

2. How do you make all properties of an interface optional?

Candidates should know that using a partial mapped type can make all properties in TypeScript optional. They might write down the Partial utility type during the interview or explain how it works in TypeScript.

Send candidates a more advanced TypeScript coding test to determine how well they navigate the language’s complex features and adapt to basic programming tools. This assessment is suitable for professionals with two to three years of experience with TypeScript. 

3. Explain how optional chaining works.

Optional chaining enables developers to safely access properties and call methods without causing errors when encountering null or undefined values.

Candidates should know that developers can use this feature to avoid runtime errors if the property or method has a null or undefined value. This can help them write cleaner, more efficient code that is less error-prone.

4. What is the difference between type inference and contextual typing?

Type inference enables the TypeScript compiler to determine the type of a variable based on the value it is initialized with. For example, the compiler would determine that a variable initialized with a value of “10” is a number.

On the other hand, contextual typing enables the compiler to determine an expression’s type based on its location and surrounding context.

Candidates who have significant experience with TypeScript should be able to list the differences between these features quickly.

5. How do you compile TypeScript with Visual Studio Code?

Top candidates will be able to show their experience with the popular code editor Visual Studio Code.

To compile TypeScript with this application, they have to ensure TypeScript is installed on their system. Then they need to open their TypeScript file and create a tsconfig.json file in the root directory of their project.

Next, they should open Visual Studio Code’s integrated terminal, navigate to the directory the TypeScript file is located in, and run the tsc command to compile the file.

Why should you use TypeScript interview questions after sending skills tests?

You should conduct interviews after sending each candidate a skills assessment that features TypeScript-related tests.

This technique ensures you choose candidates with programming skills and relevant work experience. It’s important to build a skills assessment that focuses on the candidate’s ability to write code and solve common software problems. 

For example, you might give candidates a Critical Thinking test to better understand their analytical mindset and deductive reasoning. You could also use our Reading Comprehension test to see how they make connections in code or process written information on a page. 

Once candidates have completed the tests, you can compare their responses to determine which ones deserve an interview. Our skills tests show each candidate’s score as a percentage to help you compare them easily.

Hire talented computer professionals using TypeScript interview questions 

Planning your interviews is the next step in the hiring process. You can choose which questions apply to the candidates you’re interviewing. For example, if they already have significant programming experience, questions from the advanced list are probably more appropriate. 

Before you conduct interviews, remember to gather results from skills assessments. TestGorilla has a comprehensive test library containing a range of beginner, intermediate, and advanced programming skills tests for candidates. You can sign up for a free 30-minute live demo to learn more about TestGorilla’s features and assessments. 

Hire talented computer professionals with our list of TypeScript interview questions and skills tests to gain a deeper insight into your candidates’ capabilities.

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