JavaScript Logical Operators

Understanding AND, OR, and NOT operators for complex conditions

🧠 What are Logical Operators?

Logical operators are used to combine or modify boolean values. They help you create complex conditions by combining multiple comparisons. 


// Basic logical operator example
let age = 25;
let hasLicense = true;
let canDrive = age >= 18 && hasLicense;
console.log(canDrive); // true

Output:

true

Logical Operators

&&

AND Operator

Both conditions must be true 

true && true // true
||

OR Operator

At least one condition must be true 

true || false // true
!

NOT Operator

Reverses the boolean value 

!true // false
??

Nullish Coalescing

Returns right side if left is null/undefined 

null ?? "default" // "default"

🔹 AND Operator (&&)

The AND operator returns true only when both conditions are true: 

let isWeekend = true;
let isRaining = false;

console.log(isWeekend && !isRaining); // true (weekend AND not raining)
console.log(isWeekend && isRaining);  // false (weekend but raining)

// Practical example
let age = 20;
let hasID = true;
let canEnterClub = age >= 18 && hasID;
console.log("Can enter club:", canEnterClub);

Output:

true

false

Can enter club: true

🔹 OR Operator (||)

The OR operator returns true when at least one condition is true: 

let isMember = false;
let hasDiscount = true;

console.log(isMember || hasDiscount); // true (has discount)

// Default values with OR
let username = "";
let displayName = username || "Guest";
console.log("Welcome,", displayName);

// Multiple conditions
let isHoliday = false;
let isSick = true;
let isVacation = false;
let stayHome = isHoliday || isSick || isVacation;
console.log("Stay home:", stayHome);

Output:

true

Welcome, Guest

Stay home: true

🔹 NOT Operator (!)

The NOT operator flips the boolean value: 

let isLoggedIn = false;
let needsLogin = !isLoggedIn;
console.log("Needs login:", needsLogin);

// Double NOT for boolean conversion
let value = "hello";
let isBoolean = !!value; // converts to boolean
console.log("Is truthy:", isBoolean);

// Practical example
let isOffline = false;
let canSync = !isOffline;
console.log("Can sync data:", canSync);

Output:

Needs login: true

Is truthy: true

Can sync data: true

🔹 Complex Logical Expressions

Combining multiple logical operators: 

// User access control
let age = 25;
let isEmployee = true;
let isManager = false;
let hasPermission = true;

// Complex condition
let canAccessSystem = (age >= 18 && isEmployee) || 
                     (isManager && hasPermission);

console.log("System access:", canAccessSystem);

// Parentheses for clarity
let canEditContent = isEmployee && (isManager || hasPermission);
console.log("Can edit:", canEditContent);

Output:

System access: true

Can edit: true

🧠 Test Your Knowledge

What does true && false || true return?