implement our own `new` keyword

mynew.js

const myNew = (constructor, ...args) => {
  // 1. create an object based on constructor.prototype
  const obj = Object.create(constructor.prototype)
  // 2. run constructor with this set to the above object
  const result = constructor.call(obj, ...args)

  // 3. if return value is object, user that. if not use the newly created one
  if (result instanceof Object) {
    return result
  }
  return obj
}