← ACARA Digital Technologies Years 7–8

The boolean data type: true and false

A data type with only two values, true or false, written in lowercase with no quotes. Comparisons like 5 > 3 give a boolean, and true is not the same as the string "true".

Part of: ACARA Digital Technologies Years 7–8 — Programming with Control Structures and Functions (JavaScript) — Module 14

Understanding The boolean data type: true and false in ACARA Digital Technologies Years 7–8

What it does: false is a boolean keyword. It is lowercase and has no quotation marks around it. Putting quotes around true makes it text, so typeof reports string instead of boolean. A boolean holds only true or false.

Common mistakes: Boolean values must be lowercase. True with a capital T is not defined and causes a ReferenceError. It should be let isReady = true;. Quotes turn true into a string, so typeof would print string instead of boolean. A boolean is written without quotes: let isHappy = true;.

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This module's key terms are also in a printable crossword (Modules 562–580) and word search (Modules 522–580).

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Each concept is reinforced from every angle — learned, then applied, then tested.

Learning

Duo

Which line stores a boolean value?

let isRaining = "true";let isRaining = true;

Matches

let isOpen = True;

↓

Booleans must be lowercase. True with a capital T is not a boolean, so JavaScript gives a ReferenceError. Write true.

Applying

Meanings

Term

boolean

Meaning

A data type with only two values, true or false, written in lowercase with no quotes. Comparisons like 5 > 3 give a boolean, and true is not the same as the string "true".

Practice

let isRaining = true;

Testing

Gaps

let isRaining = ;

Check Answer

Spots

2let passed = score >= 5;

3let isReady = True;

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Quick Questions

1. Which line stores a boolean value?

A. let isRaining = true; ✓

B. let isRaining = "true";

Quotes turn true into a string. A boolean is written as true with no quotes.

2. Which is a valid boolean value in JavaScript?

A. false ✓

B. False

Boolean values must be lowercase: true and false. False with a capital F is not a boolean.

3. What is the data type of true?

A. string

B. boolean ✓

typeof true gives "boolean". Only "true" in quotes would be a string.

4. What does this log? console.log(typeof "false");

A. boolean

B. string ✓

The quotes make "false" a string, even though the word looks like a boolean.

5. What value does 5 > 3 give?

A. true ✓

B. "true"

A comparison gives a boolean, true, not a string.

Match the Pairs

let isRaining = true; → Stores a yes/no value in a variable as a boolean

let isAdult = age >= 18; → Stores the boolean result of a comparison

A boolean is written in lowercase with no quotes → let gameOver = false;

true and "true" are different: one is a boolean, the other is a string → console.log(typeof "true");

let isOpen = True; → Booleans must be lowercase. True with a capital T is not a boolean, so JavaScript gives a ReferenceError. Write true.

let isFinished = "false"; → The quotes turn false into a string, not a boolean. Remove the quotes and write false.

Key Term

boolean

A data type with only two values, true or false, written in lowercase with no quotes. Comparisons like 5 > 3 give a boolean, and true is not the same as the string "true".

Fill in the Blanks

1. let isRaining = true;

Hint: Type the boolean value that means yes, in lowercase with no quotes.

2. console.log(typeof false); // boolean

Hint: Type the name of the data type that only holds two values.

3. let age = 20; let canVote = age >= 18;

Hint: Type the comparison operator that checks if age is at least 18.

4. console.log(true === "true"); // false

Hint: Type the strict equality operator to compare a boolean with a string.

5. let score = 72; let isPassing = score > 50; console.log(isPassing);

Hint: Type the variable name that stores the result of the comparison.

Spot the Error

Question 1

A let score = 10;

B let passed = score >= 5;

C let isReady = True;

D console.log(isReady);

Line C — Boolean values must be lowercase. True with a capital T is not defined and causes a ReferenceError. It should be let isReady = true;

Question 2

A let isHappy = "true";

B console.log(isHappy);

C console.log(typeof isHappy);

Line A — Quotes turn true into a string, so typeof would print string instead of boolean. A boolean is written without quotes: let isHappy = true;

Question 3

A let age = 14;

B let canVote = "age >= 18";

C console.log(canVote);

Line B — Inside quotes the comparison is just text, so it is never worked out. Without the quotes, age >= 18 gives the boolean false.

Question 4

A let isOn = true;

B let count = 0;

C let isDone = fasle;

D console.log(isDone);

Line C — false is spelled wrong. JavaScript sees fasle as a variable name that does not exist and gives a ReferenceError. It should be false.

Question 5

A let temp = 30;

B let isHot = temp > 25;

C console.log("isHot");

D console.log(typeof isHot);

Line C — Quotes make console.log print the words isHot instead of the boolean stored in the variable. It should be console.log(isHot); which prints true.

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