用JS实现队列、循环队列与任务调度

class Queue {
  #items = {};
  #head = 0;
  #tail = 0;
  enqueue(item) { this.#items[this.#tail++] = item; }
  dequeue() {
    if (this.isEmpty()) return null;
    const item = this.#items[this.#head];
    delete this.#items[this.#head++];
    return item;
  }
  isEmpty() { return this.#head === this.#tail; }
  get size() { return this.#tail - this.#head; }
}

// 循环队列（固定大小）
class CircularQueue {
  constructor(k) {
    this.items = new Array(k);
    this.capacity = k;
    this.head = 0;
    this.tail = 0;
    this.count = 0;
  }
  enqueue(item) {
    if (this.count === this.capacity) return false;
    this.items[this.tail] = item;
    this.tail = (this.tail + 1) % this.capacity;
    this.count++;
    return true;
  }
  dequeue() {
    if (this.count === 0) return null;
    const item = this.items[this.head];
    this.head = (this.head + 1) % this.capacity;
    this.count--;
    return item;
  }
}

JS队列应用：JS事件循环中的任务队列(macroTaskQueue/microTaskQueue)、异步请求并发控制(p-limit)、BFS遍历、消息队列、日志缓冲。