best-queue

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Introduction

best-queue let you control tasks in a queue.

It's easy to execute task one by one with interval time in queue like this:

Queue -> task -> wait(interval) -> task -> wait(interval) -> task -> finish

How about adding async task in queue:

Queue -> Promise.resolve(task) -> wait(interval) -> Promise.resolve(task) -> wait(interval) -> Promise.resolve(task) -> finish

What if we want to execute two tasks at the same time to support concurrency in queue:

Queue -> Promise.all([Promise.resolve(task), Promise.resolve(task)]) -> wait(interval) -> Promise.all([Promise.resolve(task), Promise.resolve(task)]) -> wait(interval) -> Promise.all([Promise.resolve(task), Promise.resolve(task)]) -> finish

But if one async task takes too much time because of network reason, the batch of task need to wait until the slow task resolve, we can do something make queue more efficient in theory.

That's best-queue do. See image below.

Install

type in the command line to install with:

npm i best-queue

Usage

Import as an ES Module:

import { createQueue } from "best-queue";

Require in Node:

const { createQueue } = require("best-queue");

Use Script source(Exposed BQueue as global var):

<script src="https://cdn.jsdelivr.net/npm/best-queue"></script>
<script src="https://unpkg.com/best-queue"></script>

API

Attribute/Method	Description	Type	Default
createQueue	create a queue	(tasks: unkonwn[], options: Options) => Promise
options	create a queue by options	Object	{ max: 1, interval: 0, recordError: false }
options.max	max concurrence task at the same time, default and min to 1	Number	1
options.interval	the interval time between tow tasks(milliscond), default to 0	Number	0
options.recordError	record error task instead of reject queue when task gone error	Boolean	false
pause()	pause the queue, queue stop to execute task	Function(): void
resume()	rerun the queue	Function(): void
subscribe(listener: Listener)	listener fired a task done	Function(({taskStatus: 'success' | 'error', data: unknown, taskIndex: number, progress: number}) => void): () => void

Example

import { createQueue } from "best-queue";

// simulate async task
function asyncTask() {
  return new Promise((resolve) => {
    setTimeout(() => {
      resolve(1);
    }, 1000);
  });
}

const asyncTasks = [asyncTask, asyncTask];

/**
 * createQueue returns enhanced promise
 */
const queue = createQueue(asyncTasks, {
  max: 1,
  interval: 1 * 1000,
  recordError: false,
});

queue.then((result) => {
  console.log(result);
});

const unsubscribe = queue.subscribe(({ taskIndex }) => {
  // queue will be paused after first task
  taskIndex === 0 && queue.pause();
});

setTimeout(() => {
  // queue paused after first task done, it will rerun the queue
  queue.resume();
}, 1500);

Lisence

Copyright (c) 2020 Jacano Licensed under the MIT license.