Writing first JavaScript program - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this JavaScript code?

Look at this code snippet. What will it print to the console?

Javascript

console.log('Hello, ' + 'world!');

A Hello, world!

B Hello,world!

C Hello world!

D SyntaxError

💡 Hint

Remember how string concatenation works with the + operator.

The + operator joins the two strings exactly as written, including the comma and space inside the first string.

❓ Predict Output

intermediate

What will this code output?

Check this code and choose the correct console output.

Javascript

let x = 5;
console.log(x * 2);

A 10

B 52

C x * 2

D undefined

💡 Hint

Multiplying a number by 2 doubles it.

Variable x holds 5, so x * 2 equals 10, which is printed.

❓ Predict Output

advanced

What is the output of this code with a function?

What will this program print when run?

Javascript

function greet(name) {
  return `Hello, ${name}!`;
}
console.log(greet('Alice'));

A greet(Alice)

B Hello, name!

C Hello, Alice!

D SyntaxError

💡 Hint

The function uses template strings to insert the name.

The function greet returns a greeting with the name inserted. Calling greet('Alice') returns 'Hello, Alice!'.

❓ Predict Output

advanced

What does this code print?

Look at this code using let and const. What is the output?

Javascript

const greeting = 'Hi';
let name = 'Bob';
console.log(greeting + ', ' + name + '!');

A ReferenceError

B Hi, Bob!

C greeting, name!

D Hi Bob!

💡 Hint

Variables greeting and name hold strings that are joined with commas and spaces.

The + operator joins the strings exactly as written, including the comma and space.

❓ Predict Output

expert

What is the output of this code with asynchronous behavior?

What will this code print to the console?

Javascript

console.log('Start');
setTimeout(() => console.log('Middle'), 0);
console.log('End');

A

Middle
Start
End

B

Start
Middle
End

C

End
Start
Middle

D

Start
End
Middle

💡 Hint

setTimeout with 0 delay still runs after the current code finishes.

The synchronous console.log calls run first, printing 'Start' then 'End'. The setTimeout callback runs last, printing 'Middle'.