TypeScript Interview Questions & Answers
Beginner Level Questions
Explore the fundamentals of TypeScript with our collection of essential beginner-level questions.
Advance Level Questions
Deepen your TypeScript knowledge with our advanced questions that cover state management and cross-platform compatibility.
Expert Level Questions
Master TypeScript with our expert-level questions that delve into performance optimization and the inner workings of the TypeScript bridge.
Question 1:- What is TypeScript, and why use it?
Answer: - **TypeScript** is a strongly typed superset of JavaScript developed by Microsoft.
- **Benefits**:
- Adds static types to JavaScript, helping catch errors during development.
- Offers better tooling with autocompletion, navigation, and refactoring.
- Supports modern JavaScript features that may not yet be supported in all browsers.Question 2:- How do you compile a TypeScript file?
Answer: - **Compilation**:
- Use the TypeScript Compiler (tsc) to compile TypeScript files.
- Run `tsc filename.ts` to generate a JavaScript file.
- **Configuration**:
- A `tsconfig.json` file can be used to configure project-wide settings.Question 3:- What are the main differences between TypeScript and JavaScript?
Answer: - **TypeScript**:
- Supports static typing.
- Includes interfaces and generics.
- Requires compilation to JavaScript.
- **JavaScript**:
- Dynamically typed.
- No interfaces or generics by default.
- Interpreted directly by browsers.Question 4:- How do you define a variable in TypeScript?
Answer: - **Variable Declaration**:
- Use `let`, `const`, or `var` keywords, similar to JavaScript.
- Specify a type explicitly if needed: `let count: number = 10;`
- **Type Inference**:
- TypeScript can infer types based on initial values: `let name = 'TypeScript';`Question 5:- What are interfaces in TypeScript?
Answer: - **Interfaces**:
- Define a contract for objects, specifying property names and types.
- Can be used to ensure objects adhere to a particular shape.
- **Example**:
```typescript
interface User {
name: string;
age: number;
}
const user: User = { name: 'Alice', age: 30 };
```Question 6:- What are classes in TypeScript?
Answer: - **Classes**:
- Provide a blueprint for creating objects.
- Support features like inheritance, access modifiers, and decorators.
- **Example**:
```typescript
class Animal {
name: string;
constructor(name: string) {
this.name = name;
}
makeSound(): void {
console.log('Sound...');
}
}
```Question 7:- Explain the concept of modules in TypeScript.
Answer: - **Modules**:
- Allow organizing code into separate files and namespaces.
- Support export and import keywords to share code between files.
- **Example**:
```typescript
// file1.ts
export function greet() {
console.log('Hello');
}
// file2.ts
import { greet } from './file1';
greet();
```Question 8:- What are generics in TypeScript?
Answer: - **Generics**:
- Provide a way to create reusable components that can work with any data type.
- Allow developers to define a placeholder for types that will be specified later.
- **Example**:
```typescript
function identity<T>(arg: T): T {
return arg;
}
const num = identity<number>(42);
const str = identity<string>('TypeScript');
```Question 9:- What are type aliases in TypeScript?
Answer: - **Type Aliases**:
- Create a new name for a type, simplifying complex type definitions.
- Can be used with any type, including primitives, arrays, and objects.
- **Example**:
```typescript
type Point = {
x: number;
y: number;
};
const origin: Point = { x: 0, y: 0 };
```Question 10:- How does TypeScript handle null and undefined?
Answer: - **Handling**:
- TypeScript has strict null checks that can be enabled in the `tsconfig.json`.
- Types can include `null` and `undefined` as possible values.
- **Example**:
```typescript
let maybe: string | null = null;
maybe = 'hello';
```Question 11:- What is the keyof operator in TypeScript?
Answer: - **keyof Operator**:
- A type query that produces a union of literal types representing the keys of a given object type.
- **Example**:
```typescript
type Person = { name: string; age: number };
type PersonKeys = keyof Person; // 'name' | 'age'
```Question 12:- Explain the difference between interface and type alias in TypeScript.
Answer: - **Interface**:
- Primarily used to define the shape of an object.
- Supports extension via the `extends` keyword.
- **Type Alias**:
- Can define any type, including primitives, unions, and tuples.
- Cannot be extended but can intersect other types.
- **Example**:
```typescript
interface Dog {
breed: string;
}
type Cat = { color: string };
```Question 13:- What is type inference in TypeScript?
Answer: - **Type Inference**:
- TypeScript automatically infers the type of a variable based on its value.
- Reduces the need for explicit type annotations.
- **Example**:
```typescript
let count = 10; // inferred as number
let message = 'Hello'; // inferred as string
```Question 14:- How do you create an enum in TypeScript?
Answer: - **Enums**:
- Enums allow defining a set of named constants.
- Can be numeric or string-based.
- **Example**:
```typescript
enum Direction {
North,
South,
East,
West
}
let heading: Direction = Direction.North;
```Question 15:- What is the purpose of the unknown type in TypeScript?
Answer: - **Unknown Type**:
- A safer version of the `any` type.
- Requires explicit type checking before performing operations on variables of this type.
- **Example**:
```typescript
let value: unknown = 'Hello';
if (typeof value === 'string') {
console.log(value.toUpperCase());
}
```Question 16:- Explain the use of the never type in TypeScript.
Answer: - **Never Type**:
- Represents the type of values that never occur.
- Typically used for functions that throw exceptions or never return.
- **Example**:
```typescript
function error(message: string): never {
throw new Error(message);
}
```Question 17:- What are decorators in TypeScript?
Answer: - **Decorators**:
- Special types of declarations that can be attached to classes and methods to modify their behavior.
- Experimental feature, enabled via `experimentalDecorators` in `tsconfig.json`.
- **Example**:
```typescript
function log(target: any, key: string) {
console.log(key + ' was called');
}
class Person {
@log
sayHello() {
console.log('Hello');
}
}
```Question 18:- What are utility types in TypeScript?
Answer: - **Utility Types**:
- Built-in types that provide common type transformations.
- Examples include `Partial<T>`, `ReadOnly<T>`, and `Pick<T, K>`.
- **Example**:
```typescript
interface Task {
title: string;
description: string;
}
const task: Partial<Task> = { title: 'Study TypeScript' };
```Question 19:- Explain the concept of union types in TypeScript.
Answer: - **Union Types**:
- Allow a variable to hold more than one type.
- Use the pipe (`|`) symbol to define union types.
- **Example**:
```typescript
let value: string | number;
value = 'Hello';
value = 42;
```Question 20:- What is the difference between an abstract class and an interface in TypeScript?
Answer: - **Abstract Class**:
- Can have both concrete and abstract methods.
- Supports access modifiers and can have instance fields.
- **Interface**:
- Only describes the shape of an object.
- Cannot have implementation details or instance fields.
- **Example**:
```typescript
abstract class Animal {
abstract makeSound(): void;
}
interface Bird {
fly(): void;
}
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