Conditional statements

The if statement

The if statements runs code based on a condition.

js

let isMembershipActive = true

if (isMembershipActive) {
  console.log('Member can borrow books.')
}

output

Member can borrow books.

The else statement

The else statement executes a block of code when the condition in the if statement is false.

js

let isMembershipActive = true

if (isMembershipActive) {
  console.log('Member can borrow books.')
} else {
  console.log('Membership is inactive. Please renew.')
}

output

Membership is inactive. Please renew.

The else if statement

The else if statement allows us to perform additional checks.

js

let userAge = 25

if (userAge < 18) {
  console.log('User is a minor.')
} else if (userAge >= 18 && userAge <= 65) {
  console.log('User is an adult.')
} else {
  console.log('User is a senior.')
}

output

User is an adult.

The ternary operator

The ternary operator provides a shorthand way of writing conditional expressions. It has three operands, separated by a question mark ? and a colon :.

condition ? (runs if condition true) : (runs if condition false)

We could use this to concisely check book availability:

js

let availableBooks = 3

let message =
  availableBooks > 0 ? 'Books are available.' : 'Books are out of stock.'

console.log(message)

output

Books are available.