array.includes(searchElement, fromIndex);

const fruits = ["Apple", "Banana", "Orange"];

console.log(fruits.includes("Banana"));   // true
console.log(fruits.includes("Mango"));    // false

const colors = ["Red", "Green", "Blue"];

console.log(colors.includes("Red"));      // true
console.log(colors.includes("red"));      // false (case sensitive)

const mixed = [1, "hello", true, null, undefined, NaN];

console.log(mixed.includes(1));            // true 
console.log(mixed.includes("hello"));      // true 
console.log(mixed.includes(true));         // true 
console.log(mixed.includes(null));         // true 
console.log(mixed.includes(undefined));    // true 
console.log(mixed.includes(NaN));          // true (special case) 

const users = [
  { id: 1, name: "Alice" },
  { id: 2, name: "Bob" },
  { id: 3, name: "Charlie" }
];

 // includes() checks for reference, not value 
const user = { id: 1, name: "Alice" };
console.log(users.includes(user));         // false (different object reference) 

 // This works because same reference 
const alice = users[0];
console.log(users.includes(alice));        // true 

const allowedRoles = ["admin", "user", "moderator"];
const userRole = "user";

console.log(allowedRoles.includes(userRole));   // true 

 // Check if user has ANY of these roles 
const userRoles = ["editor", "viewer"];
const hasPermission = userRoles.some(role => allowedRoles.includes(role));
console.log(hasPermission);   // false 

string.includes(searchString, position);

const message = "Hello World";

console.log(message.includes("World"));    // true 
console.log(message.includes("world"));    // false (case sensitive) 
console.log(message.includes("Hello"));    // true 
console.log(message.includes("xyz"));      // false 

const text = "JavaScript is awesome";

console.log(text.includes("is"));          // true 
console.log(text.includes("is", 5));       // true (search from index 5) 
console.log(text.includes("is", 15));      // false (no "is" after index 15) 

const email = "user@example.com";
console.log(email.includes("@"));          // true 

const url = "https://www.google.com";
console.log(url.includes("https://"));     // true 
console.log(url.includes("google"));       // true 

const sentence = "The quick brown fox jumps over the lazy dog";

console.log(sentence.includes("quick"));   // true 
console.log(sentence.includes("fox"));     // true 
console.log(sentence.includes("cat"));     // false 

const text = "JavaScript";

 // includes() is case sensitive, so convert both to same case 
console.log(text.toLowerCase().includes("javascript"));   // true 
console.log(text.toUpperCase().includes("JAVASCRIPT"));   // true 

function isValidCountry(country) {
  const allowedCountries = ["USA", "Canada", "Mexico", "UK", "Germany"];
  return allowedCountries.includes(country);
}

console.log(isValidCountry("USA"));        // true 
console.log(isValidCountry("France"));     // false 

const user = {
  name: "Alice",
  permissions: ["read", "write", "delete"]
};

function canPerformAction(user, action) {
  return user.permissions.includes(action);
}

console.log(canPerformAction(user, "write"));    // true 
console.log(canPerformAction(user, "admin"));    // false 

const products = [
  { id: 1, name: "Laptop", category: "Electronics" },
  { id: 2, name: "Desk", category: "Furniture" },
  { id: 3, name: "Monitor", category: "Electronics" }
];

function searchProducts(products, keyword) {
  return products.filter(product => 
    product.name.toLowerCase().includes(keyword.toLowerCase()) ||
    product.category.toLowerCase().includes(keyword.toLowerCase())
  );
}

console.log(searchProducts(products, "electronics"));
// Returns: [Laptop, Monitor]

function checkContent(text) {
  const bannedWords = ["spam", "hate", "violence"];
  
  const lowerText = text.toLowerCase();
  
  for (let word of bannedWords) {
    if (lowerText.includes(word)) {
      return `Content contains banned word: "${word}"`;
    }
  }
  
  return "Content is clean";
}

console.log(checkContent("This is great content"));    // Content is clean
console.log(checkContent("Stop spam now"));            // Content contains banned word: "spam"

function isValidFileType(filename) {
  const allowedExtensions = [".jpg", ".png", ".pdf", ".doc"];
  return allowedExtensions.some(ext => filename.toLowerCase().includes(ext));
}

console.log(isValidFileType("image.jpg"));     // true 
console.log(isValidFileType("document.pdf"));  // true 
console.log(isValidFileType("video.mp4"));     // false 

const todoList = ["Buy milk", "Clean room", "Buy bread", "Code"];

 // Filter out items containing "Buy" 
const remainingTodos = todoList.filter(task => !task.includes("Buy"));

console.log(remainingTodos);   // ["Clean room", "Code"] 

const arr = [1, 2, 3, NaN];

 // includes() - returns boolean 
console.log(arr.includes(2));               // true 
console.log(arr.includes(NaN));             // true 

 // indexOf() - returns index or -1 
console.log(arr.indexOf(2));                // 1 
console.log(arr.indexOf(NaN));              // -1 (can't find NaN) 

 // find() - returns element or undefined 
console.log(arr.find(x => x === 2));        // 2 
console.log(arr.find(x => x === 4));        // undefined 

const text = "JavaScript";

 // includes() - returns boolean 
console.log(text.includes("Script"));       // true 

 // indexOf() - returns index or -1 
console.log(text.indexOf("Script"));        // 4 

 // search() - returns index or -1 (supports regex) 
console.log(text.search(/script/i));        // 4 

 // includes() handles NaN correctly 
const arr = [NaN];
console.log(arr.includes(NaN));      // true 
console.log(arr.indexOf(NaN));       // -1 (doesn't find NaN) 
console.log(NaN === NaN);            // false (but includes finds it) 

const arr = [1, 2, 3];
console.log(arr.includes(2, -2));    // true (searches from index 1) 
console.log(arr.includes(1, -2));    // false (no element 1 from index 1) 

const words = ["hello", "", "world"];
console.log(words.includes(""));      // true 

const text = "hello world";
console.log(text.includes(""));       // true (empty string is in every string) 

const sparse = [1, , 3];
console.log(sparse.includes(undefined));  // false (empty slot ≠ undefined)

class User {
  constructor(name, roles) {
    this.name = name;
    this.roles = roles;
  }
  
  hasRole(role) {
    return this.roles.includes(role);
  }
  
  hasAnyRole(...roles) {
    return roles.some(role => this.roles.includes(role));
  }
  
  hasAllRoles(...roles) {
    return roles.every(role => this.roles.includes(role));
  }
}

const user = new User("Alice", ["user", "editor", "moderator"]);

console.log(user.hasRole("editor"));            // true 
console.log(user.hasRole("admin"));             // false 
console.log(user.hasAnyRole("admin", "editor"));  // true 
console.log(user.hasAllRoles("user", "editor"));  // true