Example of a visitor pattern in js

gistfile1.txt

// Visitor Pattern
// Some existing raw data to be altered
const cars = [
  ["Ford Escort", 10000, 50],
  ["Fiat Panda", 20000, 42],
  ["VW Polo", 25000, 59],
  ["BMW 320", 100000, 10],
  ["Dodge Viper", 200000, 3],
  ["Honda Civic", 21000, 33]
];

// The main Car object coordinates the changes
const Car = props => {
  let {name, value, stock} = props;

  const ifc = {
    update: change => change(ifc), // Special methods invoke existing ones for the update
    // Set of standard functions for processing existing data
    getName: () => name,
    getValue: () => value,
    getStock: () => stock,
    setValue: price => value = price,
    setStock: qty => stock = qty
  }
  return ifc;
};

// Special methods to apply
const Discounted = () => car => car.setValue(car.getValue()*0.8);
const HighStock = () => car => car.setStock(car.getStock()*2);

// Test cycle
const test = () => {
  // Create a list of elements using the raw input data
  const carMap = cars.map(([name, value, stock]) => Car({name, value, stock}))

  // Special methods utilized here
  const discountedValue = Discounted();
  const extraStock = HighStock();

  // Apply the changes and show the result
  for (const vehicle of carMap) {
    vehicle.update(discountedValue);
    vehicle.update(extraStock);
    console.log(
      vehicle.getName() + " now costs only $" +
      vehicle.getValue() + " and " +
      vehicle.getStock() + " cars available"
    );
  }
}

test();