Logical operator !

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Quick Questions

Shade in the A or B circle for each question.

1. What does !true give?

A true

B false

2. What does !false give?

A false

B true

3. How do you read the ! operator in plain English?

A not

B and

4. Which line is true when score is 40: !(score >= 50) or (score >= 50)?

A !(score >= 50)

B (score >= 50)

5. Which code correctly reverses the whole comparison?

A !(age > 12)

B !age > 12

Match the Pairs

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

Left column		Right column
1!true		Alet failed = !(mark >= 50);
2!(score >= 50)		BThe ! is placed before score only, not before the whole bracketed comparison. It flips score first, not the result of score >= 50.
3Put ! before brackets to reverse the result of a whole comparison		Clet isOpen = !isClosed;
4Reading ! as 'not': let isOpen be the opposite of isClosed		DGives false, because ! reverses the boolean value
5if (!score >= 50) {		E!false reverses false into true, not false. The programmer forgot that ! flips the value.
6let isNight = !false; // want false		FTrue when score is NOT 50 or more, so score is below 50

Definitions

Fill in the Blanks

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

console.log(_true);

let isDone = false; console.log(_isDone);

let score = 40; let failed = _(score >= 50); console.log(failed);

let isOpen = true; let isClosed = !______; console.log(isClosed);

let raining = false; if (!_______) console.log("Go outside");

Spot the Error

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

Question 1

A let score = 42;

B let failed = !score >= 50;

C console.log(failed);

Question 2

A let isOpen = true;

B let isClosed = ~isOpen;

C console.log(isClosed);

Question 3

A let age = 15;

B let isAdult = age >= 18;

C if (!isAdult {

D console.log("Minor");

E }

Question 4

A let score = 30;

B let target = 50;

C let passed = score >= target;

D let failed = !!passed;

E console.log(failed);

Question 5

A let hasTicket = true;

B let late = false;

C if (hasTicket && late!) {

D console.log("Enter");

E }

Answer Key

Logical operator !

Section A: Quick Questions

B — false

B — true

A — not

A — !(score >= 50)

A — !(age > 12)

Section B: Match the Pairs

!true → Gives false, because ! reverses the boolean value

!(score >= 50) → True when score is NOT 50 or more, so score is below 50

Put ! before brackets to reverse the result of a whole comparison → let failed = !(mark >= 50);

Reading ! as 'not': let isOpen be the opposite of isClosed → let isOpen = !isClosed;

if (!score >= 50) { → The ! is placed before score only, not before the whole bracketed comparison. It flips score first, not the result of score >= 50.

let isNight = !false; // want false → !false reverses false into true, not false. The programmer forgot that ! flips the value.

Section C: Definitions

! — The not operator. It reverses a boolean: !true is false and !false is true. Put it before a value or bracket, like !(score >= 50). Read it as 'not'.

Section D: Fill in the Blanks

console.log(!true);

let isDone = false;
console.log(!isDone);

let score = 40;
let failed = !(score >= 50);
console.log(failed);

let isOpen = true;
let isClosed = !isOpen;
console.log(isClosed);

let raining = false;
if (!raining) console.log("Go outside");

Section E: Spot the Error

B — Without brackets, ! only reverses score, not the whole comparison. Put the comparison in brackets: !(score >= 50).

B — The symbol for 'not' in JavaScript is !, not ~. It should be !isOpen so true becomes false.

C — The closing bracket of the if condition is missing. It should be if (!isAdult) {.

D — Two ! symbols reverse the boolean twice, so failed would just equal passed. Use one !, read as 'not': !passed.

C — The ! operator goes before the value, not after it. It should be !late, read as 'not late'.