CodeSubmit Interview Series

12 Best TypeScript Interview Questions in 2023

Need to hire TypeScript developers? Then, you need the best TypeScript interview questions. And today, we share 12 questions you can use right away. Want to learn more? Read on!

TypeScript interviews

TypeScript is a programming language created by Microsoft. It’s a strict synthetical superset of JavaScript with optional static typing added. In other words, existing JavaScript programs are valid TypeScript programs. TypeScript is used to develop large applications for both client-side and server-side execution. 

But how do you choose the right TypeScript developer? Here below are our 12 top Typescript interview questions for junior and senior developers. 

Beginner TypeScript interview questions

What interview questions should you ask junior developers? These questions are ideal for less experienced candidates who don’t have as much in-depth technical knowledge compared to more senior candidates. 

1. What is TypeScript? How does it relate to JavaScript? 


Typescript is an open-source superset of JavaScript. It focuses on strong typing and advanced language constructs to write client and server-side code with fewer errors. It’s cross-platform and is compatible with every major browser and JavaScript framework. 

This language also lets you define your own types (string, number, and Boolean) in an object-oriented manner. The compiler then checks your code against those types and flags problems before it moves on to a production environment. 

The way TypeScript relates to JavaScript is that all JavaScript libraries and syntax work, but TypeScript adds more syntax options and compiler features that aren’t found in JavaScript. In the same way, TypeScript can interact with many similar technologies like jQuery and Angular. 

2. What are the advantages of TypeScript? 


TypeScript is simple, easy to learn, and fast. It’s expressive and has, therefore, less syntactical clutter. TypeScript is also easy to debug thanks to its advanced debugging features that focus on catching logical errors before compile time.

Thanks to static typing, TypeScript is easier to read and more structured than JavaScript’s dynamic typing. It’s also usable across platforms on client-side and server-side projects thanks to versatile transpiling. 

3. What is the difference between JavaScript and TypeScript? 


TypeScript is a superset of JavaScript, while JavaScript is a scripting language. TypeScript also has an interface concept; something JavaScript doesn’t have.

TypeScript doesn’t run in the same browser as JavaScript and it has classes, while JavaScript has functions. JavaScript doesn’t support modules, which TypeScript does.

4. What are the most important TypeScript features? 


The most important TypeScript features are: 

  • ES6 features: Includes most features of planned ECMAScript 2015, such as Arrow functions. 

  • Cross-platform: Its compiler can be installed on any operating system, including Windows, Linux, and macOS. 

  • Static type-checking: TypeScript helps type checking at compile time by using static typing. This enables you to find compile-time errors while you’re writing the code without running the script. 

  • Optional static typing: TypeScript enables optional static typing for those who are used to dynamic typing in JavaScript. 

  • Object-oriented language: TypeScript offers standard OOP features like interfaces, modules, and classes. 

  • DOM Manipulation: TypeScript can be used to manipulate the DOM for adding or removing client-side web page elements.

Advanced TypeScript interview questions

What are some more advanced TypeScript interview questions? Here are questions to ask senior TypeScript developers. 

5. What are type assertions in TypeScript?


Type assertion works in the same way as typecasting in other languages, essentially as a soft version of typecasting. What it means is that type assertion suggests that the compiler sees the variable as a certain type, but it doesn’t force it into that mold. However, type checking and restructuring of data, which are possible in languages like C# and Java, are not possible in TypeScript. Type assertion doesn’t have an impact on runtime and it’s used purely in the compiler. 

6. How do you use TypeScript Mixins? 


Mixins are inheritance that works in the opposite direction. They allow you to build new classes by combining simpler partial class setups from previous classes. For instance, instead of class A extending class B to gain functionality, class B takes from class A and returns a new class with additional functionality. 

7. What’s a .map file? How do you use it? 


A map file is a source map that shows how the original TypeScript code has been interpreted into usable JavaScript code. Map files simplify debugging, as you can catch odd compiler behavior. These files can also be used, with the help of debugging tools, to edit the underlying TypeScript instead of the emitted JavaScript file. 

8. What is JSX in TypeScript? 


With TypeScript, you can embed, type check, and compile JSX directly to JavaScript. JSX is an XML-like syntax that can be embedded and that allows you to create HTML. 

9. What are Arrow or lambda functions? 


Arrow functions in TypeScript are similar to lambda functions in other languages. This function is a shorthand syntax for defining function expressions of anonymous functions and it lets you skip the function keyword and write more concise code. 

10. What are the different scopes in TypeScript?


The different scopes in TypeScript are: 

  • Global Scope: Can be used anywhere in the program. Global Scope is defined outside of any class. 

  • Local Scope/Code Block: These variables are defined in the local scope. They can be used anywhere in a block. 

  • Function/Class Scope: These variables are defined in a function or class. They can be used anywhere within that scope. 

11. How do you make all interface properties optional? 


Partial mapped types can be used to easily make all properties optional.   

12. How do you use TypeScript for the backend? 


With Node.js, you can use TypeScript for backend work. Install the TypeScript compiler into Node.js with this command: 

npm i -g typescript 

Over to you!

There you have it! Now you know what the 12 top TypeScript interview questions are. 

But interviews are only one part of your recruitment process. You also need to assess your candidates’ technical skills. How? With a skill assessment tool.

That’s what we offer at CodeSubmit. You can easily set up proven skill assessments that candidates complete online. 

Want to learn more? 

Try CodeSubmit for free today (no credit card required).