zaraz/lib/zaraz.js

Cheap way to introduce short async delay.

import Debug from 'debug';

const debug = Debug('zaraz');

const queues = {
  timer: undefined,
  index: 0,
  current: [],
  later: []
};

class Item {
  #fn;
  #params;
  constructor(fn, params) {
    this.#fn = fn;
    this.#params = params;
  }

  run() {
    // bail if nothing to run
    if (!this.#fn) return;

    const fn = this.#fn;
    this.clear();
    fn(...this.#params);
  }

  clear() {
    this.#fn = undefined;
  }
}

export default function zaraz(fn, ...params) {
  const item = new Item(fn, params);
  const q = queues.index > 0 ? queues.later : queues.current;
  q.push(item);

  kick();
  return item;
}

zaraz.DELAY = 10; // default delay
zaraz.ACTIVE = 100; // how long before we yield after processing items
zaraz.MAX_ITEMS = 1000; // how many items we can process in a single step

function execute() {
  const start = Date.now();
  const max = Math.min(queues.current.length, queues.index + zaraz.MAX_ITEMS);

  debug('queues before', queues.current.length - queues.index, queues.later.length);

  while (queues.index < max) {
    queues.current[queues.index++].run();
    if (Date.now() - start > zaraz.ACTIVE) {
      debug('breaking...');
      break;
    }
  }

  debug('queues after', queues.current.length - queues.index, queues.later.length);

  if (queues.index === queues.current.length) {
    queues.current = queues.later;
    queues.later = [];
    queues.index = 0;
  }

  kick();
}

function kick() {
  const empty = queues.current.length === 0;
  if (empty && queues.timer) {
    // no timer needed since there is nothing more to do
    clearInterval(queues.timer);
    queues.timer = undefined;
    return;
  }
  if (!empty && !queues.timer) {
    // things to do and no timer
    queues.timer = setInterval(execute, zaraz.DELAY);
  }
}