JavaScript If Else & Conditional Logic

// Basic if statement
let age = 18;
if (age >= 18) {
    console.log("You are an adult");
}

// If...else statement
if (age >= 18) {
    console.log("You can vote");
} else {
    console.log("You cannot vote yet");
}

// If...else if...else chain
let score = 85;
if (score >= 90) {
    console.log("Grade: A");
} else if (score >= 80) {
    console.log("Grade: B");
} else if (score >= 70) {
    console.log("Grade: C");
} else if (score >= 60) {
    console.log("Grade: D");
} else {
    console.log("Grade: F");
}

// Nested if statements
let isLoggedIn = true;
let hasPermission = false;

if (isLoggedIn) {
    if (hasPermission) {
        console.log("Access granted");
    } else {
        console.log("Access denied - insufficient permissions");
    }
} else {
    console.log("Please log in first");
}

// Ternary operator (shorthand)
let status = age >= 18 ? "adult" : "minor";
let message = `You are an ${status}`;

// Multiple conditions with logical operators
let isStudent = true;
let hasDiscount = false;
let age2 = 25;

if (isStudent && age2 < 30) {
    hasDiscount = true;
    console.log("Student discount applied");
} else if (age2 >= 65) {
    hasDiscount = true;
    console.log("Senior discount applied");
} else {
    console.log("No discount available");
}

// Modern conditional patterns (2025)
// Optional chaining with conditionals
let user = {
    profile: {
        settings: {
            notifications: true
        }
    }
};

if (user?.profile?.settings?.notifications) {
    console.log("Notifications are enabled");
} else {
    console.log("Notifications are disabled or not configured");
}

// Nullish coalescing with conditionals
let theme = user?.profile?.settings?.theme ?? 'light';
console.log(`Current theme: ${theme}`);

// Short-circuit evaluation
let isAdmin = user?.role === 'admin';
let canEdit = isAdmin || user?.permissions?.includes('edit');

if (canEdit) {
    console.log("User can edit content");
}

// Conditional object properties
let config = {
    apiUrl: 'https://api.example.com',
    timeout: 5000,
    ...(isAdmin && { debugMode: true }),
    ...(user?.preferences?.theme && { theme: user.preferences.theme })
};

// Conditional function calls
let logger = {
    info: (msg) => console.log(`[INFO] ${msg}`),
    error: (msg) => console.error(`[ERROR] ${msg}`),
    debug: (msg) => console.debug(`[DEBUG] ${msg}`)
};

let logLevel = 'info';
let message = 'User logged in';

if (logLevel === 'debug') {
    logger.debug(message);
} else if (logLevel === 'error') {
    logger.error(message);
} else {
    logger.info(message);
}

// Switch-like pattern with objects
const actions = {
    'create': () => console.log('Creating...'),
    'read': () => console.log('Reading...'),
    'update': () => console.log('Updating...'),
    'delete': () => console.log('Deleting...')
};

let action = 'create';
if (actions[action]) {
    actions[action]();
} else {
    console.log('Invalid action');
}

// Exercise: Build a Grade Calculator
function calculateGrade(score) {
    if (score >= 90) {
        return 'A';
    } else if (score >= 80) {
        return 'B';
    } else if (score >= 70) {
        return 'C';
    } else if (score >= 60) {
        return 'D';
    } else {
        return 'F';
    }
}

// Exercise: Build a User Access Control System
function checkAccess(user, resource) {
    // Check if user exists and is active
    if (!user || !user.isActive) {
        return { allowed: false, reason: 'User not found or inactive' };
    }
    
    // Check if user has required permissions
    if (!user.permissions || !user.permissions.includes(resource)) {
        return { allowed: false, reason: 'Insufficient permissions' };
    }
    
    // Check if user is admin (bypass all restrictions)
    if (user.role === 'admin') {
        return { allowed: true, reason: 'Admin access' };
    }
    
    // Check time-based restrictions
    const currentHour = new Date().getHours();
    if (currentHour < 6 || currentHour > 22) {
        return { allowed: false, reason: 'Access restricted outside business hours' };
    }
    
    return { allowed: true, reason: 'Access granted' };
}

// Test the functions
console.log(calculateGrade(95)); // 'A'
console.log(calculateGrade(85)); // 'B'
console.log(calculateGrade(75)); // 'C'
console.log(calculateGrade(55)); // 'F'

const user1 = {
    id: 1,
    name: 'John',
    isActive: true,
    role: 'user',
    permissions: ['read', 'write']
};

const user2 = {
    id: 2,
    name: 'Admin',
    isActive: true,
    role: 'admin',
    permissions: ['read', 'write', 'delete']
};

console.log(checkAccess(user1, 'read')); // { allowed: true, reason: 'Access granted' }
console.log(checkAccess(user2, 'delete')); // { allowed: true, reason: 'Admin access' }
console.log(checkAccess(null, 'read')); // { allowed: false, reason: 'User not found or inactive' }