Logical Operators in JavaScript

Logical operators let you combine multiple conditions into a single expression.

AND (&&)

Returns true only if both conditions are true:

let age = 25;
let hasLicense = true;

if (age >= 18 && hasLicense) {
    console.log("You can drive!");
}

// Truth table:
// true  && true  → true
// true  && false → false
// false && true  → false
// false && false → false

OR (||)

Returns true if at least one condition is true:

let day = "Saturday";

if (day === "Saturday" || day === "Sunday") {
    console.log("It's the weekend!");
}

// Truth table:
// true  || true  → true
// true  || false → true
// false || true  → true
// false || false → false

NOT (!)

Flips a boolean value:

let isLoggedIn = false;

if (!isLoggedIn) {
    console.log("Please log in.");
}

console.log(!true);   // false
console.log(!false);  // true
console.log(!"");     // true (empty string is falsy)
console.log(!"hello"); // false (non-empty string is truthy)

Combining Operators

let age = 25;
let isStudent = true;
let hasID = true;

if ((age >= 18 && hasID) || isStudent) {
    console.log("Access granted!");
}

Short-Circuit Evaluation

// && returns the first falsy value (or the last value)
let name = "" && "Alice";  // "" (empty string is falsy)

// || returns the first truthy value (or the last value)
let user = "" || "Guest";  // "Guest"
let port = undefined || 3000;  // 3000