| /* | |
| How it works: | |
| `this.#head` is an instance of `Node` which keeps track of its current value and nests another instance of `Node` that keeps the value that comes after it. When a value is provided to `.enqueue()`, the code needs to iterate through `this.#head`, going deeper and deeper to find the last value. However, iterating through every single item is slow. This problem is solved by saving a reference to the last value as `this.#tail` so that it can reference it to add a new value. | |
| */ | |
| class Node { | |
| value; | |
| next; | |
| constructor(value) { | |
| this.value = value; | |
| } | |
| } | |
| export default class Queue { | |
| #head; | |
| #tail; | |
| #size; | |
| constructor() { | |
| this.clear(); | |
| } | |
| enqueue(value) { | |
| const node = new Node(value); | |
| if (this.#head) { | |
| this.#tail.next = node; | |
| this.#tail = node; | |
| } else { | |
| this.#head = node; | |
| this.#tail = node; | |
| } | |
| this.#size++; | |
| } | |
| dequeue() { | |
| const current = this.#head; | |
| if (!current) { | |
| return; | |
| } | |
| this.#head = this.#head.next; | |
| this.#size--; | |
| // Clean up tail reference when queue becomes empty | |
| if (!this.#head) { | |
| this.#tail = undefined; | |
| } | |
| return current.value; | |
| } | |
| peek() { | |
| if (!this.#head) { | |
| return; | |
| } | |
| return this.#head.value; | |
| // TODO: Node.js 18. | |
| // return this.#head?.value; | |
| } | |
| clear() { | |
| this.#head = undefined; | |
| this.#tail = undefined; | |
| this.#size = 0; | |
| } | |
| get size() { | |
| return this.#size; | |
| } | |
| * [Symbol.iterator]() { | |
| let current = this.#head; | |
| while (current) { | |
| yield current.value; | |
| current = current.next; | |
| } | |
| } | |
| * drain() { | |
| while (this.#head) { | |
| yield this.dequeue(); | |
| } | |
| } | |
| } | |