Unary operators in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code using unary plus?

Consider the following JavaScript code. What will be printed to the console?

Javascript

let a = '5';
let b = +a;
console.log(typeof b, b);

A undefined 5

B string 5

C number 5

D object 5

💡 Hint

Unary plus converts strings to numbers.

The unary plus operator converts the string '5' to the number 5, so typeof b is 'number' and b is 5.

❓ Predict Output

intermediate

What is the output of this code using unary negation?

Look at this code snippet. What will it print?

Javascript

let x = 10;
console.log(-x);

A -10

B 10

C NaN

D undefined

💡 Hint

Unary negation changes the sign of a number.

The unary negation operator changes 10 to -10.

❓ Predict Output

advanced

What is the output of this code using prefix and postfix increment?

What will this code print to the console?

Javascript

let i = 3;
console.log(i++);
console.log(++i);

A

4
5

B

4
4

C

3
4

D

3
5

💡 Hint

Postfix returns the value then increments; prefix increments then returns.

i++ prints 3 then increments to 4; ++i increments to 5 then prints 5.

❓ Predict Output

advanced

What is the output of this code using the typeof unary operator?

What will this code print?

Javascript

let val = null;
console.log(typeof val);

A null

B object

C undefined

D boolean

💡 Hint

typeof null is a known JavaScript quirk.

In JavaScript, typeof null returns 'object' due to legacy reasons.

❓ Predict Output

expert

What is the output of this code combining unary plus and logical NOT?

What will this code print to the console?

Javascript

let a = '0';
console.log(+!a);

A 0

B 1

C NaN

D false

💡 Hint

Logical NOT converts to boolean then negates; unary plus converts boolean to number.

The string '0' is truthy, so !a evaluates to false. The unary plus converts false to the number 0.