TypeScript has become a must-have skill for today’s web and mobile developers. It helps you write safer, clearer, and more maintainable code that actually scales.
This guide brings together 100 essential TypeScript interview questions and answers. It’s designed to help developers strengthen their understanding and get ready for real-world interviews.
You’ll find topics from type systems and interfaces to decorators and generics. This collection makes it easier to review both core and advanced features.
Each question highlights the concepts behind TypeScript’s design. You’ll see how they actually come up in technical interviews and everyday development.
1. What is TypeScript, and why use it?
TypeScript is a programming language from Microsoft. It extends JavaScript by adding static types, so you can catch errors while coding instead of after you ship.
Since it compiles down to regular JavaScript, you can run TypeScript anywhere JavaScript works. That’s pretty handy.
Developers use TypeScript to write more reliable and maintainable code. The type system brings better code completion, easier refactoring, and clearer documentation—right in your editor.
Teams especially benefit when projects get big or complex. TypeScript supports modern JavaScript features and adds stuff like interfaces, generics, and enums.
These extras make code clearer and more structured. Here’s a quick peek:
let message: string = "Hello, TypeScript!";
console.log(message);This simple example shows how TypeScript asks for type definitions. It makes your intent obvious and helps avoid type-related bugs.
2. Explain TypeScript’s type system.
TypeScript uses a static type system. This means you can catch mistakes before you even run your code.
By defining the types of variables, parameters, and functions, you reduce surprises at runtime. That makes your code easier to maintain and refactor.
The type system covers basics like string, number, and boolean. It also handles complex types: arrays, tuples, and enums.
You can create custom types with interfaces and type aliases. That keeps things clear and consistent across a project.
TypeScript uses type inference, so it figures out types for you when it can. You can also use union, intersection, and generic types for more flexibility.
function addNumbers(a: number, b: number): number {
return a + b;
}Here, the compiler checks that both parameters are numbers. It stops you from using the wron