The boolean data type: true and false

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. Which line stores a boolean value?

A let isRaining = true;

B let isRaining = "true";

2. Which is a valid boolean value in JavaScript?

A false

B False

3. What is the data type of true?

A string

B boolean

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

A boolean

B string

5. What value does 5 > 3 give?

A true

B "true"

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1let isRaining = true;		Alet gameOver = false;
2let isAdult = age >= 18;		BStores the boolean result of a comparison
3A boolean is written in lowercase with no quotes		Cconsole.log(typeof "true");
4true and "true" are different: one is a boolean, the other is a string		DBooleans must be lowercase. True with a capital T is not a boolean, so JavaScript gives a ReferenceError. Write true.
5let isOpen = True;		EThe quotes turn false into a string, not a boolean. Remove the quotes and write false.
6let isFinished = "false";		FStores a yes/no value in a variable as a boolean

Definitions

boolean

Fill in the Blanks

Complete each line of code by filling in the missing parts.

let isRaining = ____;

console.log(typeof false); // _______

let age = 20; let canVote = age __ 18;

console.log(true ___ "true"); // false

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

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A let score = 10;

B let passed = score >= 5;

C let isReady = True;

D console.log(isReady);

Question 2

A let isHappy = "true";

B console.log(isHappy);

C console.log(typeof isHappy);

Question 3

A let age = 14;

B let canVote = "age >= 18";

C console.log(canVote);

Question 4

A let isOn = true;

B let count = 0;

C let isDone = fasle;

D console.log(isDone);

Question 5

A let temp = 30;

B let isHot = temp > 25;

C console.log("isHot");

D console.log(typeof isHot);

Answer Key

The boolean data type: true and false

Section A: Quick Questions

A — let isRaining = true;

A — false

B — boolean

B — string

A — true

Section B: 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.

Section C: Definitions

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".

Section D: Fill in the Blanks

let isRaining = true;

console.log(typeof false); // boolean

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

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

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

Section E: Spot the Error

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

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

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

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

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.