Essential TypeScript Interview Questions — PART — 3

In modern development, TypeScript has become a staple for ReactJS, NodeJS, and Angular applications. Here are some crucial TypeScript questions you might encounter in an interview.

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11. What is a String enum?

String enums hold string values:

enum allDirections {
  North = "North",
  East = "East",
  South = "South",
  West = "West"
};
let currentDirection = allDirections.North; // "North"

12. What are Type Aliases?

Type aliases define custom types:

type Year = number;
type Car = { year: Year, type: string, model: string };
const car: Car = { year: 2005, type: "Tata", model: "Tiago" };

13.What are interfaces?

Interfaces define object shapes:

interface Square {
  length: number;
}
const square: Square = { length: 20 };

14.How to extend interfaces?

Use the extends keyword:

interface Square {
  length: number;
}
interface ColorSquare extends Square {
  color: string;
}
const square: ColorSquare = { length: 20, color: 'blue' };

15.What are Union types?

Union types allow variables to hold multiple types:

function printSuccessCode(code: string | number) {
  console.log(`My success code is ${code}.`);
}
printSuccessCode(200);
printSuccessCode('200');