Logical Operators

Logical operators are used to combine multiple conditions.

&& (Logical AND)

This returns true only when all conditions are true.

console.log(true && true);   // true
console.log(true && false);  // false

But in JavaScript, it does not always return true/false. It returns actual values.

console.log(5 && 10);   // 10
console.log(0 && 10);   // 0

How it works:

• It checks left → right
• If it finds a falsy value, it stops and returns it
• If all are true, it returns the last value

Falsy values:

false, 0, “”, null, undefined, NaN

Example:

let age = 20;
let hasID = true;
console.log(age >= 18 && hasID); // true

|| (Logical OR)

This returns true if at least one condition is true.

console.log(true || false); // true
console.log(false || false); // false

But again, it returns actual values:

console.log(0 || 10);   // 10
console.log(5 || 10);   // 5

How it works:

• It checks left → right
• Returns the first truthy value
• If none found, returns last value

Example:

let userName = "" || "Guest";
console.log(userName); // "Guest"

! (Logical NOT)

This reverses the boolean value.

console.log(!true);  // false
console.log(!false); // true

It first converts value to boolean, then reverses it:

console.log(!0);     // true
console.log(!"Hello"); // false

Double NOT is often used to convert any value into boolean:

console.log(!!"Hello"); // true
console.log(!!0);       // false