JavaScript Booleans


What is a Boolean?

In JavaScript, a Boolean represents one of two values:

  • true
  • false

Booleans are mainly used to make decisions in code — like controlling if something happens or not.


Creating Booleans


1. Boolean Literals

let isJavaScriptFun = true;
let isSkyGreen = false;

2. Using the Boolean() Function

let x = Boolean(10); // true
let y = Boolean(0); // false
let z = Boolean(""); // false
let a = Boolean("Hello"); // true

The Boolean() function converts any value to true or false.


Examples and Outputs


Example 1: Simple Booleans

let isAdult = true;
let isChild = false;
console.log(isAdult); // Output: true
console.log(isChild); // Output: false

Example 2: Boolean Conversion

console.log(Boolean(100)); // Output: true
console.log(Boolean(0)); // Output: false
console.log(Boolean("Hi")); // Output: true
console.log(Boolean("")); // Output: false
console.log(Boolean(undefined)); // Output: false
console.log(Boolean(null)); // Output: false

Truthy and Falsy Values

JavaScript considers some values automatically as true (truthy) and others as false (falsy).

Falsy Values Means
false
false false
0 false
-0 false
"" (Empty string) false
null false
undefined false
NaN false

Everything else is considered truthy (means true).


Boolean in Conditional Statements

Booleans are very important in if, while, and other conditions.

Example:

let isLoggedIn = true;
if (isLoggedIn) {
console.log("Welcome back!");
} else {
console.log("Please log in.
");
}
// Output: Welcome back!

Comparison Operations (Return Boolean)

Operators like == , === , >, <, etc., return a boolean.

Example:

console.log(10 > 5); // Output: true
console.log(3 ===
"3"); // Output: false
console.log(3 ==
"3"); // Output: true (because == does type
conversion)
Logical Operators with Booleans
Operator Description Example Output

Logical Operators with Booleans

Operator Description Example Output
&& (AND) Both must be true true && false false
` ` (OR) At least one true
! (NOT) Reverses boolean !true false

Example:

console.log(true && false); // Output: false
console.log(true || false); // Output: true
console.log(!true);