Operators and strings · Lesson 6 of 45

Comparison and logic

===, !==, &&, || and ??.

8 minutes4 games

Comparisons return true or false: >, <, >=, <=, === (exactly equal) and !== (not equal).

Always use ===, not ==. == converts types before comparing and causes surprises, like 0 == "" being true.

JavaScript

console.log(5 === 5)     // true
console.log(5 === "5")   // false: different types
console.log(5 == "5")    // true: converted, avoid
console.log("apple" < "banana") // true: dictionary order

Logical operators

Operator	Meaning	Example
`&&`	and: both must be true	`age >= 18 && hasId`
`\|\|`	or: one is enough	`isAdmin \|\| isOwner`
`!`	not	`!isLoggedIn`
`??`	fallback if `null` or `undefined`	`name ?? "Guest"`

JavaScript

const age = 20
const hasTicket = true
console.log(age >= 18 && hasTicket) // true

const nickname = null
console.log(nickname ?? "Guest")     // Guest

const count = 0
console.log(count || 10)  // 10: 0 is falsy
console.log(count ?? 10)  // 0: only null/undefined are replaced

What's the output?

console.log(true && false)
console.log(true || false)
console.log(!true)

What will this code print?

Quick question

What is "3" === 3?

Complete the code

Print true if the age is from 13 to 19 (a teen).

const age = 16
console.log(age >= 13  age <= 19)

Exercise

Print username, or Anonymous if it's missing (use ??).

Expected output: Anonymous

JavaScript

const username = undefined

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JavaScript

Operators and strings · Lesson 6 of 45

Comparison and logic

===, !==, &&, || and ??.

8 minutes4 games

Comparisons return true or false: >, <, >=, <=, === (exactly equal) and !== (not equal).

Always use ===, not ==. == converts types before comparing and causes surprises, like 0 == "" being true.

JavaScript

console.log(5 === 5)     // true
console.log(5 === "5")   // false: different types
console.log(5 == "5")    // true: converted, avoid
console.log("apple" < "banana") // true: dictionary order

Logical operators

Operator	Meaning	Example
`&&`	and: both must be true	`age >= 18 && hasId`
`\|\|`	or: one is enough	`isAdmin \|\| isOwner`
`!`	not	`!isLoggedIn`
`??`	fallback if `null` or `undefined`	`name ?? "Guest"`

JavaScript

const age = 20
const hasTicket = true
console.log(age >= 18 && hasTicket) // true

const nickname = null
console.log(nickname ?? "Guest")     // Guest

const count = 0
console.log(count || 10)  // 10: 0 is falsy
console.log(count ?? 10)  // 0: only null/undefined are replaced

What's the output?

console.log(true && false)
console.log(true || false)
console.log(!true)

What will this code print?

Quick question

What is "3" === 3?

Complete the code

Print true if the age is from 13 to 19 (a teen).

const age = 16
console.log(age >= 13  age <= 19)

Exercise

Print username, or Anonymous if it's missing (use ??).

Expected output: Anonymous

JavaScript

const username = undefined

Learn more from

Played 0 of 4 games