Backoff.js

class Backoff {
  constructor(min = 500, max, jitter = true) {
    this.min = min;
    this.max = max !== null ? max : min * 10;
    this.jitter = jitter;

    this._current = min;
    this._timeout = null;
    this._fails = 0;
  }

  get fails() {
    return this._fails;
  }

  get current() {
    return this._current;
  }

  get pending() {
    return this._timeout !== null;
  }

  succeed() {
    this.cancel();
    this._fails = 0;
    this._current = this.min;
  }

  fail(callback) {
    this.fails += 1;
    let delay = this._current * 2;
    if (this.jitter) delay *= Math.random();
    this._current = Math.min(this._current + delay, this.max);
    if (callback !== null) {
      if (this._timeout !== null) throw new Error('callback already pending');
      this._timeout = setTimeout(() => {
        try {
          if (callback !== null) callback();
        } finally {
          this._timeout = null;
        }
      }, this._current);
    }
    return this._current;
  }

  cancel() {
    if (this._timeout !== null) {
      clearTimeout(this._timeout);
      this._timeout = null;
    }
  }
}