RequestQueue

RequestQueue.js

class RequestQueue {
  constructor() {
    this.interval = 1000;
    this.size = 10;
    this.queue = [];
    this.intervalToken = null;
    this.runningCount = 0;
  }

  enqueue(url) {
    this.queue.unshift(url);
    this._dequeue();
  }

  _dequeue() {
    if (this.intervalToken) return;

    this.intervalToken = setInterval(() => {
      if (!this.queue.length) {
        clearInterval(this.intervalToken);
        return;
      }
      while (this.runningCount < this.size && this.queue.length) {
        const url = this.queue.pop();
        this.runningCount++;
        this._makeRequest(url)
          .then(() => {
            this.runningCount--;
          })
          .catch(() => {
            this.runningCount--;
          });
      }
    }, this.interval);
  }

  _makeRequest(url) {
    return this._sleep(Math.random() * 1000);
  }

  _sleep(ms) {
    return new Promise(resolve => {
      setTimeout(resolve, ms);
    });
  }
}