模組

// IIFE Goal: Create a new scope, return the data just once. All of data inside IIFE will be private as it would inside the fn scope. 
// Using this way, we don't need to call it separately. And it ensures its called only once.
// IIFE is created only once, goal is 'NOT TO REUSE' by executing it multiple times.

// Result of running an IIFE is stored, or else it will disappear simply.
const ShoppingCart2 = (function(){
  const cart = [];
  const shippingCost = 10;
  const totalPrice = 237;
  const totalQuantity = 10;

  const addToCart = function(product, quantity){
    cart.push({product, quantity});
    console.log(`${quantity} ${product} added to cart. Shipping cost is ${shippingCost}`);
  };

  const orderStock = function(product, quantity){
    console.log(`${quantity} ${product} ordered from supplier`);
  };
  // Need to return something, in order to return a public API. For that, an object is returned containing stuff which needs to be made public.
  return {
    addToCart,
    cart, 
    totalPrice,
    totalQuantity
  };
})();
// Everything inside the above module is private to the module.
// The above fn returns the object mentioned inside return statement and assign it to the ShoppingCart2 variable mentioned at the start of fn. This IIFE is returned then long ago.
// All this is possible because of closures. Hence, addToCart can acccess the cart variable.

ShoppingCart2.addToCart('apple', 4);
ShoppingCart2.addToCart('pizza', 5);
ShoppingCart2;
ShoppingCart2.shippingCost; // inaccessible.

// EXPORT
export.addToCart = function(product, quantity){
    cart.push({product, quantity});
    console.log(`${quantity} ${product} added to cart. Shipping cost is ${shippingCost}`);
};

// IMPORT: is similar to ES Modules but would use a require fn.
// require is not defined in browser env but its defined in node env as its a part of commonjs
const addToCart = require('./shoppingCart.js')