Logical Operators: AND, OR, NOT

Sometimes one question isn't enough. You need to combine several. To ride a rollercoaster, you need to be tall enough and have a ticket. To get a discount, you need to be a student or a senior citizen.

JavaScript has three logical operators for combining booleans:

(The || symbol is two "pipe" characters. On most keyboards, the pipe | is on the same key as the backslash \, above Enter. You'll need Shift to type it.)

AND: &&

Both conditions have to be true:

const height = 140;
const hasTicket = true;

const canRide = height >= 120 && hasTicket;
console.log(canRide);

true

OR: ||

At least one condition has to be true:

const isStudent = false;
const isSenior = true;

const getsDiscount = isStudent || isSenior;
console.log(getsDiscount);

true

NOT: !

! flips a boolean to its opposite. It's like the word "not" in English:

const isRaining = false;
console.log(!isRaining);
console.log(!true);
console.log(!!true);

true
false
true

!isRaining reads as "not raining," which is true here because it isn't raining. And !!true flips twice, back to true again. (Like saying "I'm not not hungry.")

Combining them

You can combine these operators to ask more complicated questions. Use parentheses to keep things clear:

const age = 25;
const hasLicense = true;
const isDrunk = false;

const canDrive = age >= 18 && hasLicense && !isDrunk;
console.log(canDrive);

const isWeekend = true;
const isHoliday = false;
const isSunny = true;
const goToBeach = (isWeekend || isHoliday) && isSunny;
console.log(goToBeach);

true
true

Read the second one out loud: "If it's the weekend or a holiday, and it's sunny, go to the beach." Code that reads like a sentence is good code.