Lesson 7 - Booleans

JavaScript Logical Conditions and Booleans

Booleans are special values in JavaScript that can only be true or false (always lowercase!). They are often used with logical conditions to control how your program runs.

// Boolean values
let x = true;
let y = false;
console.log(x, y);

// Simple if with boolean
let isHungry = true;
if (isHungry) {
console.log("Time to eat!");
}

Comparison Operators:

Equal	`a === b`	Not Equal	`a !== b`
Greater than	`a > b`	Less than	`a < b`
Greater than or equal	`a >= b`	Less than or equal	`a <= b`

💡 In JavaScript use three equal signs === to compare values. A single = stores a value in a variable.

// Comparisons give booleans
console.log(5 > 3); // true
console.log(10 === 5); // false
console.log(10 !== 5); // true

Checking a list with .includes() tells you if a value is a member of an array or not. It gives back true or false. Put ! in front to check that it is not in the list.

let fruits = ["apple", "cherry", "banana"];
let favorite = "chocolate";
let found = fruits.includes(favorite);
console.log(found);

Boolean Operators used to combine the values of multiple boolean values.

let age = 6;
let height = 52;
let isAllowed = (age >= 8 || height >= 48);
console.log(isAllowed);
let notAllowed = !isAllowed;
console.log(notAllowed);

&& - true if both conditions are true.
|| - true if one of the conditions is true.
! - flips the result.

Tip: Conditions let your program make decisions. Try changing the values and see how the program follows different paths.

True or False?

console.log(10 > 5);
console.log(2 === 3);

💡 Predict the output.

Check Age

let age = 15;
if (age >= 18) {
console.log("Adult");
} else {
console.log("Child");
}

💡 What will it print?

Guess favorite food

let favorite = ["Pizza", "Nasi Goreng", "Kebap", "Soto Ayam"];
let guess = "Pizza";
let found = favorite.includes(guess);
if (found) {
console.log("Yes, thats my favorite food");
}
if (!found) {
console.log("No, I don't like that");
}

💡 Change guess and make your own favorite food list.

Even or Odd?

let number = 8;
if (number % 2 === 0) {
console.log("Even");
} else {
console.log("Odd");
}

💡 Try changing the number.

Pass or Fail

Store an exam score in a variable. If it’s 60 or higher, print "Pass"

let score = 75;
if (score >= 60) {
console.log("Pass");
}

💡 Add an else that prints "Fail", then try a score of 40.

Using &&

let temp = 25;
if (temp > 20 && temp < 30) {
console.log("Nice weather!");
} else {
console.log("Not nice.");
}

💡 Predict the output.

Using ||

let day = "Sunday";
if (day === "Saturday" || day === "Sunday") {
console.log("Weekend!");
} else {
console.log("Weekday.");
}

💡 Try changing the value of day.

Using !

let isRaining = false;
if (!isRaining) {
console.log("Go outside!");
} else {
console.log("Take an umbrella.");
}

💡 Predict the output.

If…Else if…Else

let score = 85;
if (score >= 90) {
  console.log("Excellent");
} else if (score >= 60) {
  console.log("Good");
} else {
  console.log("Try harder");
}

💡 What will it print?

Mystery Output

let x = 5;
let y = 10;
if (x * 2 === y) {
console.log("Equal!");
} else {
console.log("Not equal!");
}

❓ Predict the output without running first.

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