Frequently Asked TypeScript Interview Questions

Do you have a TypeScript technical interview coming up soon?

Providing correct answers to technical questions asked in interviews ensures your success in your job interview. Here are the most frequently asked TypeScript interview questions and their answers compiled for you. 👇

➕ TypeScript is closely related to JavaScript. Especially if you need to review interview questions related to JavaScript, you can also check out our JavaScript interview questions content.

 

Popular TypeScript Interview Questions

 

1. What is TypeScript?

TypeScript is an object-oriented, compiled programming language built on top of the JavaScript programming language. It is a superset of JavaScript designed to provide better tools at any scale. TypeScript makes JavaScript development more efficient and helps detect errors earlier.

📍 TypeScript Syntax:

 

TypeScript code is written in a file with a “.ts” extension and is then compiled to JavaScript using a compiler. You can write the file in any code editor.

 

2. What are the differences between TypeScript and JavaScript?

 

3. What are the prominent features of TypeScript?

 

• Cross-Platform: TypeScript can be installed on any operating system such as Windows, MacOS, and Linux.
• Object-Oriented: TypeScript offers features like classes, interfaces, and modules, allowing you to write object-oriented code for both server-side and client-side development.
• Static Type Checking: TypeScript can determine the types of variables and functions in advance thanks to its static type declaration feature. This allows errors to be detected at compile time and creates a safer codebase.
• ECMAScript 6+ Support: TypeScript is fully compatible with ECMAScript 6 and later versions, allowing the use of modern JavaScript features and enabling the writing of more up-to-date and advanced code.

 

4. What are the benefits of using TypeScript?

1. TypeScript is fast, simple, and easy to learn. Additionally, it can run on any browser.
2. Uses a syntax and semantics similar to JavaScript.
3. TypeScript code can be called from existing JavaScript code. It also works seamlessly with existing JavaScript frameworks and libraries.
4. Includes ES6 and ES7 features that can run on JavaScript engines at the ES5 level, such as Node.js.

 

5. What are the components of TypeScript?

The components of TypeScript are important elements used in the software development process, forming the fundamental building blocks of the language. In TypeScript, there are three different types of components including:

1️⃣ Language - Consists of syntax, keywords, and type annotations.

2️⃣ TypeScript Compiler - This compiler (tsc) converts code written in TypeScript to JavaScript code, enabling TypeScript to run in browsers.

3️⃣ TypeScript Language Service - The TypeScript Language Service is a component that provides features and services in integrated development environments (IDEs) and text editors.

 

6. How is TypeScript installed?

There are two ways to install TypeScript tools:

1. npm (Node.js Package Manager) can be installed via the command line tool.
2. Visual Studio can be used by installing it.

 

📍 If you are using Visual Studio or VS Code IDE, the easiest way to add to these two platforms is to search for a package and add it or download it from the TypeScript website.

 

7. How are TypeScript files compiled?

TypeScript files are compiled using the TypeScript Compiler (tsc). TypeScript files have a “.ts” extension and contain code written in TypeScript language. The TypeScript Compiler is used to convert these files to JavaScript files.

Any JavaScript file is also a TypeScript file because TypeScript is a superset of JavaScript. That is, when the extension “.js” is changed to “.ts”, it becomes a TypeScript file. To compile a “.ts” file to .js, the following command is used:

 

 

✔️ Here, "file.ts", represents the name of the TypeScript file you want to compile. This command will convert the ".ts" file to a JavaScript file with the same name and a ".js" extension.

 

8. What are the built-in data types in TypeScript?

When a variable is created, the goal is to assign some value to that variable. However, what type of value can be assigned to that variable depends on the variable's data type. The built-in data types in TypeScript are the fundamental data types used to define the types of variables and values. The predefined built-in data types in TypeScript are:

 

• Number: Represents numerical data. Numbers are stored as floating-point values in TypeScript. For example: const myNum: number = 1207;
• String: Represents text or character sequences. Strings in TypeScript work the same way as in JavaScript. For example: let myString: string = 'bacon'
• Boolean: Represents a logical value. When the Boolean data type is used, the output is only true or false. For example: const myBool: boolean = false;
• Null: Represents a variable with an undefined value.
• Undefined: Represents undefined variables.
• Void: Indicates that a function does not return a value.

 

9. What are variables in TypeScript and how are they created?

A variable is a named fundamental building block used to store and use values in memory. In TypeScript, an extension of JavaScript, three different keywords are used to define variables: var, let, and const.

When declaring a variable in TypeScript, certain rules must be followed.

✅ Variable names may contain a letter or numeric digit.

✅ Variable names cannot start with a digit.

✅ They cannot contain spaces or special characters except for the underscore (_) and dollar ($) sign.

 

Below are example code snippets for variable rules.

 

10. What are the different ways to declare a variable?

📍 There are four different ways to declare a variable:

 

11. Is it possible to automatically compile .ts with real-time changes in the “.ts” file?

Yes, it is possible to automatically compile “.ts” with real-time changes in the .ts file. One of the tools that perform this operation is called "TypeScript Watch Mode."

To use Watch Mode, you can use the following command in the terminal or command prompt:

tsc --watch file1.ts

This command will watch the TypeScript files and automatically perform the compilation process when any changes occur.

 

12. What are the object-oriented terms supported by TypeScript?

TypeScript supports the following object-oriented terms:

• Modules
• Classes
• Interfaces
• Inheritance
• Data Types
• Member functions

 

13. What are interfaces in TypeScript?

An interface is the structure or skeleton of an object. In TypeScript, an interface defines the shape of an object. It includes the names of object properties, their values, and information about their data types.

Interfaces are used to ensure type safety and to make the code more understandable and maintainable. In TypeScript, interfaces are defined using the “interface” keyword.

 

📍 Example Syntax:

 

14. What are classes in TypeScript?

Classes are a common abstraction used in object-oriented programming (OOP) languages to define data structures. In TypeScript, classes specify how objects are created and what properties they have according to a predefined template. A class includes data structures like Constructor, Properties, and Methods.

 

📍 A class in TypeScript is defined as follows:

 

15. How is optional static typing done in TypeScript?

TypeScript is an optionally statically typed language. This means you can ask the compiler to ignore the type of a variable. By using any data type, you can assign any value type to the variable.

 

📍 Example:

declare const libraryName;

 

16. What are modules in TypeScript?

A module is a way to group related variables, functions, classes, and interfaces. In TypeScript, modules are structural elements that enable the code to be divided into pieces and allow each piece to function independently.

Modules make the code in large and complex projects more organized, understandable, and manageable. A module can be created using the “export” keyword. A variable, function, class, or interface exported from a different module can be imported using the “import” keyword.

 

📍 Example:

 

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

 

 

18. What is “namespace” in TypeScript?

A namespace is used to logically group functions and is also known as an internal module. This function preserves older code in TypeScript internally. In large projects, it helps make the code more organized and understandable. The main purpose is to split the code into pieces and group them under namespaces. A namespace can also include interfaces, classes, functions, and variables.

 

📍 Example Syntax:

 

19. What is the tsconfig.json file?

tsconfig.json is a file in JSON format. It specifies the root files and compiler options required to compile the project.

 

✅ The tsconfig.json file is always placed in the root directory of the project.

✅ You can customize the rules you want the TypeScript compiler to apply.

 

Example of a tsconfig.json file:

 

20. What are generics in TypeScript?

Generics in TypeScript are a mechanism for creating types and are used to provide type safety. TypeScript generics allow you to create reusable components. Generics enable the creation of components that can work with a variety of data types instead of a single type. A type parameter is written between open (<>) and closed (>) angle brackets. A special type variable that specifies types uses <T>.

 

📍 Example:

 

21. What is JSX in TypeScript?

JSX is an embeddable XML-like syntax. TypeScript allows you to embed JSX directly into JavaScript, providing type checking and compilation. It enables easier and more understandable creation of UI components.

💬 If you want to use JSX, you need to give your file a .tsx extension and enable the jsx option.

 

📍 Example:

 

 

22. How do enums work in TypeScript?

Enums are a common data structure found in many languages. In TypeScript, "enums" are a data type used to define a collection of constant values associated with a specific name. In short, enums are a way to define constant values.

🔖 Enums are used to represent specific states or values, making the code more understandable and easier to maintain.

 

Example:

 

23. When is the "declare" keyword used?

The “declare” keyword is used when using a JavaScript library within a TypeScript project that does not have declarations.

📍 Example:

declare const libraryName;

 

24. How are ‘declaration’ files automatically obtained?

 

25. How are objects created in TypeScript?

Objects are collections of key-value pairs. Objects are data structures defined as key-value pairs and can contain different data types. In TypeScript, an object type represents any value. It can be defined simply by listing its properties and their types.

 

📍 For example:

 

Next Step 

First, clarify all the basic concepts before your TypeScript interview. Many of the questions asked in the interview test your fundamental knowledge of TypeScript.

Secondly, practice! Don't just review the theory; apply TypeScript to your applications. The more you use TypeScript, the better you'll understand its concepts and various uses. If you want to learn TypeScript and build a career, TypeScript Bootcamps can add a lot to you.

Do you already have programming knowledge? Then all you need to do to reach your dream career is create your profile on Coderspace and wait for us to find the perfect opportunity for you! Click here to create your profile within 2 minutes and just sit back while we handle the rest. :)