What is TypeScript - Practice Questions & Exercises

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is TypeScript mainly used for?

TypeScript is a programming language that is a superset of JavaScript. What is its main purpose?

A To add static types and catch errors before running the code

B To style web pages with colors and layouts

C To replace HTML for building web pages

D To run JavaScript code faster in the browser

💡 Hint

Think about what TypeScript adds to JavaScript to help developers.

TypeScript adds static typing to JavaScript, which helps catch errors early during development.

❓ Predict Output

intermediate

What is the output of this TypeScript code?

Consider this TypeScript code snippet:

function greet(name: string) {
  return `Hello, ${name.toUpperCase()}!`;
}

console.log(greet("world"));

What will it print?

Typescript

function greet(name: string) {
  return `Hello, ${name.toUpperCase()}!`;
}

console.log(greet("world"));

A TypeError at runtime

B Hello, world!

C Hello, WORLD!

D SyntaxError during compilation

💡 Hint

Look at how the toUpperCase() method changes the string.

The function converts the input string to uppercase, so "world" becomes "WORLD".

❓ Predict Output

advanced

What error does this TypeScript code raise?

Look at this TypeScript code:

let age: number = "30";

What error will the TypeScript compiler show?

Typescript

let age: number = "30";

A Type 'string' is not assignable to type 'number'.

B SyntaxError: Unexpected string

C No error, code runs fine

D ReferenceError: age is not defined

💡 Hint

Check the type declared and the value assigned.

TypeScript expects a number but got a string, so it reports a type mismatch error.

🧠 Conceptual

advanced

Which feature is unique to TypeScript compared to JavaScript?

Which of these features is only available in TypeScript and not in plain JavaScript?

A Loops to repeat actions

B Functions to perform calculations

C Variables to store data

D Interfaces to define object shapes

💡 Hint

Think about features that help describe data structures before running code.

Interfaces are a TypeScript feature to describe object shapes and types, not present in JavaScript.

🚀 Application

expert

What is the value of 'result' after running this TypeScript code?

Analyze this TypeScript code:

type User = { name: string; age: number };

const users: User[] = [
  { name: "Alice", age: 25 },
  { name: "Bob", age: 30 },
  { name: "Carol", age: 35 }
];

const result = users.filter(u => u.age > 28).map(u => u.name).join(", ");

console.log(result);

What will be printed?

Typescript

type User = { name: string; age: number };

const users: User[] = [
  { name: "Alice", age: 25 },
  { name: "Bob", age: 30 },
  { name: "Carol", age: 35 }
];

const result = users.filter(u => u.age > 28).map(u => u.name).join(", ");

console.log(result);

A Alice, Bob, Carol

B Bob, Carol

C Alice

D Error: Property 'age' does not exist

💡 Hint

Look at the filter condition and what is extracted after filtering.

The code filters users older than 28, which are Bob and Carol, then joins their names with a comma.