Boolean Logic

A logical operator that returns true only if both conditions on either side are true.

Part of: JavaScript Coding without HTML and CSS — Module 12, ACARA Digital Technologies Years 7–8 — Programming with Control Structures and Functions (JavaScript) — Module 29, ACARA Digital Technologies Years 9–10 — Modular and Object-Oriented Programming (JavaScript) — Module 5

Understanding Boolean Logic in JavaScript

What it does: ! flips true to false or false to true. This requires both hasTicket and hasID to be true. || returns true as long as at least one side is true. JavaScript uses &&, not the word 'and'. Logical AND requires two ampersands: &&. Logical OR requires two pipe characters: ||. ! returns the reversed boolean value of isOpen. JavaScript's logical AND operator is &&, not 'and'.

Common mistakes: Use &&, not the word 'and', to combine conditions. Use ||, not the word 'or', to combine conditions.

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Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 11–25) and word search (Modules 1–29).

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Learning

Duo

Does && return true only if both sides are true?

YesNo

Matches

console.log(a and b);

↓

Wrong - use && instead of the word 'and'

Applying

Meanings

Term

Meaning

A logical operator that returns true only if both conditions on either side are true.

Practice

let isSunny = true;

Testing

Gaps

console.log(isSunny isWarm);

Check Answer

Spots

1console.log(a and b);

2let a = true;

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Quick Questions

1. Does && return true only if both sides are true?

A. No

B. Yes ✓

&& requires both conditions to be true to return true.

2. Does || return true if either side is true?

A. Yes ✓

B. No

|| returns true as long as at least one side is true.

3. Is 'and' a valid JavaScript operator for combining conditions?

A. No ✓

B. Yes

JavaScript uses &&, not the word 'and'.

4. Does ! reverse a boolean value?

A. Yes ✓

B. No

! flips true to false and false to true.

5. Is a single & the same as && in JavaScript?

A. Yes

B. No ✓

Logical AND requires two ampersands: &&.

Match the Pairs

isSunny && isWarm → True only if both isSunny and isWarm are true

isSunny || isWarm → True if at least one of isSunny or isWarm is true

Reverses a boolean's value → !isOpen

Combines two conditions, requiring both to be true → hasTicket && hasID

console.log(a and b); → Wrong - use && instead of the word 'and'

console.log(x or y); → Wrong - use || instead of the word 'or'

Key Term

&&

A logical operator that returns true only if both conditions on either side are true.

Fill in the Blanks

1. console.log(isSunny && isWarm);

Hint: Type the operator that returns true only if both sides are true.

2. console.log(isSunny || isWarm);

Hint: Type the operator that returns true if either side is true.

3. console.log(!isSunny);

Hint: Type the operator that reverses a boolean value.

4. let ready = hasTicket && hasID;

Hint: Type the operator that returns true only if both sides are true.

5. let closed = !isOpen;

Hint: Type the operator that reverses a boolean value.

Spot the Error

Question 1

A console.log(a and b);

B let a = true;

C let b = false;

Line A — Use &&, not the word 'and', to combine conditions.

Question 2

A let x = true;

B let y = false;

C console.log(x or y);

Line C — Use ||, not the word 'or', to combine conditions.

Question 3

A let flag = true;

B console.log(not flag);

C console.log(!flag);

Line B — Use !, not the word 'not', to reverse a boolean.

Question 4

A let p = true;

B let q = false;

C console.log(p & q);

Line C — Use &&, not a single &, for logical AND.

Question 5

A console.log(m | n);

B let m = true;

C let n = false;

Line A — Use ||, not a single |, for logical OR.

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