smart-factory.js

factory = (props, methods, proxy) => new Proxy(Object.assign(Object.create(methods), props), proxy)

DLL = (value, next=null) => {
  let props = {value, next, prev: null}
  let methods = {
    map: function (cb) {
       let result = DLL(null)
       let current = this
	   let i=0
       while(current){
          result.last = cb(current.value, i++, this)
          current = current.next
       }
       return result.next
    },
  }
  let proxy = {
    set: (obj, prop, value) => {
      if(prop == 'next') { 
        let next = DLL(value) 
        next.prev = obj
        obj.next = next
        return
      }
      if(prop == 'last'){
        let current = obj
        while(current.next) {
          current = current.next 
        }
        if(current == obj) {
	  let next = DLL(value)
	  next.prev = obj
	  current.next = next
	  return 
        }
        current.next = value
        return
      }
      obj[prop] = value
    }
  }
  return factory(props, methods, proxy)
}
  
head = DLL('first')
head.last = 'second'
head.last = 'third'
head.last = 'fourth'

doubled = head.map(v => v + '!!!!!')