What can you pass to a function as a parameter?

// Primitive - by value
function changePrimitive(num) {
  num = 100;
}
let x = 5;
changePrimitive(x);
console.log(x); // 5 (unchanged)
 
// Object - by reference
function changeObject(obj) {
  obj.name = "Changed";
}
let user = { name: "Alexander" };
changeObject(user);
console.log(user.name); // "Changed"

function processData(number, text, flag, empty, undef) {
  console.log(typeof number); // "number"
  console.log(typeof text);   // "string"
  console.log(typeof flag);   // "boolean"
  console.log(typeof empty);  // "object" (null)
  console.log(typeof undef);  // "undefined"
}
 
processData(42, "Hello", true, null, undefined);

function handleData(user, numbers, date) {
  console.log(user.name);        // "Alexander"
  console.log(numbers.length);   // 3
  console.log(date.getFullYear()); // current year
  
  // Modify object
  user.age = 30;
  numbers.push(4);
}
 
let person = { name: "Alexander" };
let arr = [1, 2, 3];
let now = new Date();
 
handleData(person, arr, now);
console.log(person.age);  // 30 (changed!)
console.log(arr.length);  // 4 (changed!)

function processArray(array, callback) {
  const result = [];
  for (let item of array) {
    result.push(callback(item));
  }
  return result;
}
 
// Pass function as parameter
const numbers = [1, 2, 3, 4, 5];
const doubled = processArray(numbers, x => x * 2);
console.log(doubled); // [2, 4, 6, 8, 10]
 
// Pass named function
function square(x) {
  return x * x;
}
const squared = processArray(numbers, square);
console.log(squared); // [1, 4, 9, 16, 25]

class User {
  constructor(name) {
    this.name = name;
  }
  
  greet() {
    return `Hello, I'm ${this.name}!`;
  }
}
 
function createInstance(Constructor, ...args) {
  return new Constructor(...args);
}
 
// Pass class as parameter
const user = createInstance(User, "Alexander");
console.log(user.greet()); // "Hello, I'm Alexander!"
 
// Pass built-in constructor
const date = createInstance(Date, 2024, 0, 1);
console.log(date.getFullYear()); // 2024

// Object destructuring
function greetUser({ name, age = 18 }) {
  return `Hello, ${name}! You are ${age} years old.`;
}
 
const user = { name: "Alexander", age: 30 };
console.log(greetUser(user)); // "Hello, Alexander! You are 30 years old."
 
// Array destructuring
function processCoordinates([x, y, z = 0]) {
  return { x, y, z };
}
 
const coords = [10, 20];
console.log(processCoordinates(coords)); // { x: 10, y: 20, z: 0 }

function sum(...numbers) {
  return numbers.reduce((total, num) => total + num, 0);
}
 
console.log(sum(1, 2, 3, 4, 5)); // 15
console.log(sum(10, 20));        // 30
 
// Mixed parameters
function logMessage(level, ...messages) {
  console.log(`[${level}]:`, ...messages);
}
 
logMessage("INFO", "User", "logged", "into", "system");
// [INFO]: User logged into system

function createUser(name = "Anonymous", age = 18, isActive = true) {
  return { name, age, isActive };
}
 
console.log(createUser());                    // { name: "Anonymous", age: 18, isActive: true }
console.log(createUser("Alexander"));         // { name: "Alexander", age: 18, isActive: true }
console.log(createUser("Maria", 25, false)); // { name: "Maria", age: 25, isActive: false }

function modifyValues(a, b) {
  a = 100;
  b.value = 100;
}
 
let num = 5;
let obj = { value: 5 };
 
modifyValues(num, obj);
console.log(num, obj.value);

function processArray(arr) {
  arr = [1, 2, 3];
  return arr;
}
 
let original = [4, 5, 6];
let result = processArray(original);
console.log(original, result);

function test(callback) {
  return callback(10, 20);
}
 
const result = test((a, b) => a + b);
console.log(result);

function createObjects(Constructor, count) {
  const objects = [];
  for (let i = 0; i < count; i++) {
    objects.push(new Constructor(`Object ${i}`));
  }
  return objects;
}
 
class Item {
  constructor(name) {
    this.name = name;
  }
}
 
const items = createObjects(Item, 3);
console.log(items.length);

function greet({ name, age = 25 }) {
  return `${name} (${age} years old)`;
}
 
console.log(greet({ name: "Alexander" }));
console.log(greet({ name: "Maria", age: 30 }));

function calculate(...numbers) {
  return numbers.filter(n => typeof n === 'number').reduce((sum, n) => sum + n, 0);
}
 
console.log(calculate(1, "2", 3, null, 4, undefined, 5));

// Bad
function createUser(userObj) {
  const name = userObj.name;
  const age = userObj.age;
  const email = userObj.email;
  // ...
}
 
// Good
function createUser({ name, age, email }) {
  // name, age, email are immediately available
}

function processData(data = [], options = {}) {
  const { sort = true, limit = 10 } = options;
  // safe work with parameters
}

// If you don't want to change the original
function processArray(arr) {
  const copy = [...arr]; // create copy
  copy.push('new element');
  return copy;
}
 
// For objects
function updateUser(user) {
  return { ...user, lastUpdated: new Date() }; // return new object
}