Logical Operators

const age = 20
const hasLicense = true
 // AND: Both must be true
if (age >= 18 && hasLicense) {
  console.log('You can drive!')  // This runs
}
 // OR: At least one must be true
if (age >= 21 || hasLicense) {
  console.log('Special access!')  // This also runs
}

// Truth table for &&
console.log(true && true)    // true
console.log(true && false)   // false
console.log(false && true)   // false
console.log(false && false)  // false
 // Real example
const age = 25
const hasID = true
 if (age >= 21 && hasID) {
  console.log('Can buy alcohol')  // Runs (both true)
}

const username = 'player1'
const password = 'secret'
const isActive = true
 if (username === 'player1' && password === 'secret' && isActive) {
  console.log('Login successful!')  // All three must be true
}
 // Can break into multiple lines for readability
if (
  username === 'player1' &&
  password === 'secret' &&
  isActive
) {
  console.log('Welcome!')
}

// Truth table for ||
console.log(true || true)    // true
console.log(true || false)   // true
console.log(false || true)   // true
console.log(false || false)  // false
 // Real example
const isWeekend = true
const isHoliday = false
 if (isWeekend || isHoliday) {
  console.log('No school!')  // Runs (one is true)
}

const role = 'admin'
 if (role === 'admin' || role === 'moderator' || role === 'owner') {
  console.log('You have special permissions!')
}
 // Example: Accept multiple payment methods
const paymentMethod = 'credit card'
 if (paymentMethod === 'credit card' ||
    paymentMethod === 'PayPal' ||
    paymentMethod === 'crypto') {
  console.log('Payment accepted!')  // Runs
}

// Reversing booleans
console.log(!true)    // false
console.log(!false)   // true
 const isLoggedIn = false
 if (!isLoggedIn) {
  console.log('Please log in')  // Runs (not logged in)
}
 const hasSubscription = true
 if (!hasSubscription) {
  console.log('Subscribe now!')  // Does NOT run
}

const age = 15
const hasPermission = false
 // NOT with AND
if (age >= 18 && !hasPermission) {
  console.log('Adult but no permission')
}
 // NOT with OR
if (!hasPermission || age < 13) {
  console.log('Access restricted')  // Runs (no permission)
}
 // Double NOT (rarely used, but good to know)
console.log(!!true)   // true (reverses twice)
console.log(!!'text') // true (converts to boolean)

const items = []
 if (!items.length) {
  console.log('Cart is empty')  // Runs (length is 0)
}
 const username = ''
 if (!username) {
  console.log('Please enter a username')  // Runs (empty string)
}
 const isVisible = true
 if (!isVisible) {
  console.log('Hidden')
} else {
  console.log('Visible')  // Runs
}