class ListIterator {

constructor(list) {

this.list = list;

}

next() {

if (this.list == List.empty) return {done: true};

let result = {value: this.list.value, done: false};

this.list = this.list.rest;

return result;

}

}

// Class mostly from the previous exercise

class List {

constructor(value, rest) {

this.value = value;

this.rest = rest;

}

toArray() {

let array = [];

for (let list = this; list != List.empty; list = list.rest) {

array.push(list.value);

}

return array;

}

get length() {

let length = 0;

for (let list = this; list != List.empty; list = list.rest) {

length++;

}

return length;

}

static fromArray(array) {

let list = List.empty;

for (let i = array.length - 1; i >= 0; i--) {

list = new List(array[i], list);

}

return list;

}

// New code:

[Symbol.iterator]() {

return new ListIterator(this);

}

}

List.empty = new List(undefined, undefined);

for (let value of List.fromArray(["a", "b", "c"])) {

console.log(value);

}

// → a

// → b

// → c