Example of factory based object creation

object-factory.js

function createProduct( initialStock ) {
  let stock = initialStock;
  
  return {
    /* ... extra fields omitted for simplicity ... */
    updateStock( newStock ) {
      stock += newStock;
    },
    getStock( ) {
      return stock;
    }
  }
};

const product = createProduct( 4 );
console.log( product.stock ); // undefined!
console.log( product.getStock( ) ); // 4
product.updateStock( 3 );
console.log( product.getStock( ) ); // 7

const product2 = createProduct( 0 );
console.log( product2.getStock( ) ); // 0