What is JavaScript - Practice Questions & Exercises

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is JavaScript used for?

JavaScript is a popular programming language. What is its main use?

A To style web pages with colors and fonts

B To create databases for storing data

C To write server operating systems

D To add interactivity and dynamic behavior to web pages

💡 Hint

Think about what happens when you click buttons or see animations on websites.

JavaScript runs in the browser to make web pages interactive, like responding to clicks or updating content without reloading.

❓ Predict Output

intermediate

What is the output of this JavaScript code?

Look at this code and choose the correct output.

Javascript

console.log(typeof []);

A "array"

B "list"

C "object"

D "undefined"

💡 Hint

In JavaScript, arrays are a type of object.

The typeof operator returns "object" for arrays because arrays are special objects in JavaScript.

❓ Predict Output

advanced

What is the output of this JavaScript code snippet?

What will this code print to the console?

Javascript

console.log(0.1 + 0.2 === 0.3);

A true

B false

C TypeError

D undefined

💡 Hint

Think about how computers handle decimal numbers.

Due to floating-point precision, 0.1 + 0.2 is not exactly 0.3, so the comparison is false.

🧠 Conceptual

advanced

Which statement about JavaScript is true?

Choose the correct statement about JavaScript.

A JavaScript supports asynchronous programming with promises and async/await.

B JavaScript is a statically typed language.

C JavaScript can only run in web browsers.

D JavaScript code must be compiled before running.

💡 Hint

Think about how JavaScript handles tasks like fetching data from the internet.

JavaScript supports asynchronous programming using promises and async/await to handle tasks without blocking the program.

❓ Predict Output

expert

What is the output of this JavaScript code with closures?

What will this code print to the console?

Javascript

function makeCounter() {
  let count = 0;
  return function() {
    count += 1;
    return count;
  };
}
const counter1 = makeCounter();
const counter2 = makeCounter();
console.log(counter1());
console.log(counter1());
console.log(counter2());

A

1
2
1

B

1
1
1

C

0
1
0

D

2
3
2

💡 Hint

Each call to makeCounter creates a new independent counter.

counter1 and counter2 have separate count variables. counter1 increments twice, then counter2 starts at 0 and increments once.