JavaScript Functions

// 1. Function Declaration — hoisted, callable before definition
function calculateGST(price) {
  return price * 0.18;
}

// 2. Function Expression — not hoisted, assigned to variable
const calculateGST2 = function(price) {
  return price * 0.18;
};

// 3. Arrow Function — concise, no own 'this'
const calculateGST3 = (price) => price * 0.18;

// All three do the same thing
console.log(calculateGST(1000));   // 180
console.log(calculateGST2(1000));  // 180
console.log(calculateGST3(1000));  // 180

// HOISTING demonstration
console.log(hoisted("World"));     // Works! ✅
function hoisted(name) { return "Hello " + name; }

// console.log(notHoisted("World")); // ❌ TypeError — not hoisted
const notHoisted = (name) => "Hello " + name;

// Basic parameters and return
function getFullName(firstName, lastName) {
  return firstName + " " + lastName;
}

// Default parameters — used when argument is missing/undefined
function createProfile(name, role = "user", verified = false) {
  return {
    name: name,
    role: role,
    verified: verified,
    createdAt: new Date().toISOString().split("T")[0]
  };
}

// Rest parameters — collect unlimited arguments
function calculateTotal(...prices) {
  return prices.reduce((sum, price) => sum + price, 0);
}

// Destructuring parameters
function displayUser({ name, email, role = "guest" }) {
  return name + " <" + email + "> [" + role + "]";
}

console.log(getFullName("Asha", "Sharma"));
console.log(createProfile("Ravi"));
console.log(createProfile("Priya", "admin", true));
console.log(calculateTotal(1299, 499, 2499, 149));
console.log(displayUser({ name: "Mira", email: "mira@example.com" }));

// Functions stored in variables (function expressions)
const greet = (name) => "Hello, " + name;

// Functions passed as arguments (callbacks)
function applyOperation(numbers, operation) {
  return numbers.map(operation);
}

const double = n => n * 2;
const square = n => n * n;
const addTax = n => +(n * 1.18).toFixed(2);

const prices = [100, 200, 300];
console.log("Doubled:", applyOperation(prices, double));
console.log("Squared:", applyOperation(prices, square));
console.log("With tax:", applyOperation(prices, addTax));

// Functions returned from functions (higher-order functions)
function createMultiplier(factor) {
  return (number) => number * factor;
}

const triple = createMultiplier(3);
const tenX = createMultiplier(10);

console.log("Triple 5:", triple(5));
console.log("10x of 7:", tenX(7));

// ─── Form Validation ──────────────────────────────────────────────
function validateEmail(email) {
  return email.includes("@") && email.includes(".") && email.length >= 5;
}

// ─── Currency Formatting ───────────────────────────────────────────
function formatINR(amount) {
  return "₹" + amount.toLocaleString("en-IN", {
    minimumFractionDigits: 2,
    maximumFractionDigits: 2
  });
}

// ─── Text Processing ───────────────────────────────────────────────
function truncate(text, maxLen = 100) {
  if (text.length <= maxLen) return text;
  return text.slice(0, maxLen).trim() + "...";
}

// ─── Date Formatting ──────────────────────────────────────────────
function formatDate(dateStr) {
  const d = new Date(dateStr);
  return d.toLocaleDateString("en-IN", {
    day: "2-digit",
    month: "short",
    year: "numeric"
  });
}

// ─── Tests ────────────────────────────────────────────────────────
console.log(validateEmail("asha@example.com"));
console.log(validateEmail("invalid-email"));
console.log(formatINR(1234567.89));
console.log(truncate("This is a very long product description that exceeds the limit", 30));
console.log(formatDate("2026-06-01"));