JavaScript Fundamentals

// Modern variable declaration
const name = "Alice";           // Use const by default
let age = 25;                   // Use let if reassignment needed
var old = true;                 // Avoid var (function-scoped, confusing)

// Types
const number = 42;
const string = "hello";
const boolean = true;
const array = [1, 2, 3];
const object = { name: "Alice", age: 25 };
const nothing = null;
const undefined_value = undefined;

// Arrow functions (modern)
const add = (a, b) => a + b;

// Traditional function
function multiply(a, b) {
  return a * b;
}

// Functions with default parameters
const greet = (name = "Guest") => `Hello, ${name}`;

// Array methods
const numbers = [1, 2, 3, 4, 5];
numbers.map(n => n * 2);        // Transform
numbers.filter(n => n > 2);     // Filter
numbers.find(n => n === 3);     // Find first

// Object destructuring
const person = { name: "Alice", age: 25 };
const { name, age } = person;

// Promises
const fetchData = () => {
  return fetch("/api/data")
    .then(response => response.json())
    .then(data => console.log(data))
    .catch(error => console.error(error));
};

// Async/await (modern, cleaner)
const getData = async () => {
  try {
    const response = await fetch("/api/data");
    const data = await response.json();
    console.log(data);
  } catch (error) {
    console.error(error);
  }
};