RX-QUEUE

Easy to Use ReactiveX Queue that Supports Delay/DelayExecutor/Throttle/Debounce Features Powered by RxJS.

Picture Credit: Queues in JavaScript

API

Class

1. RxQueue
2. DelayQueue
3. ThrottleQueue
4. DebounceQueue
5. DelayQueueExecutor

Function

1. concurrencyExecuter()

RxQueue

RxQueue is the base class of all other queues. It extends from RxJS Subject.

Example:

import { RxQueue } from 'rx-queue'

const queue = new RxQueue()
queue.next(1)
queue.next(2)
queue.next(3)

queue.subscribe(console.log)
// Output: 1
// Output: 2
// Output: 3

DelayQueue

DelayQueue passes all the items and add delays between items.

Picture Credit: ReactiveX Single Operator Delay

Practical examples of DelayQueue:

1. We are calling a HTTP API which can only be called no more than ten times per second, or it will throw a 500 error.

Example:

import { DelayQueue } from 'rx-queue'

const delay = new DelayQueue(500)  // set delay period time to 500 milliseconds
delay.subscribe(console.log)

delay.next(1)
delay.next(2)
delay.next(3)

// Output: 1
// Paused 500 millisecond...
// Output: 2
// Paused 500 millisecond...
// Output: 3

ThrottleQueue

ThrottleQueue passes one item and then drop all the following items in a period of time.

Picture Credit: ReactiveX Observable Throttle

By using throttle, we don't allow to our queue to pass more than once every X milliseconds.

Practical examples of ThrottleQueue:

1. User is typing text in a textarea. We want to call auto-save function when user is typing, and want it only run at most once every five minutes.

Example:

import { ThrottleQueue } from 'rx-queue'

const throttle = new ThrottleQueue(500)  // set period time to 500 milliseconds
throttle.subscribe(console.log)

throttle.next(1)
throttle.next(2)
throttle.next(3)

// Output: 1

DebounceQueue

DebounceQueue drops a item if there's another one comes in a period of time.

Picture Credit: ReactiveX Observable Debounce

The Debounce technique allow us to deal with multiple sequential items in a time period to only keep the last one.

Debouncing enforces that no more items will be passed again until a certain amount of time has passed without any new items coming.

Practical examples of DebounceQueue:

1. User is typing text in a search box. We want to make an auto-complete function call only after the user stop typing for 500 milliseconds.

Example:

import { DebounceQueue } from 'rx-queue'

const debounce = new DebounceQueue(500)  // set period time to 500 milliseconds
debounce.subscribe(console.log)

debounce.next(1)
debounce.next(2)
debounce.next(3)

// Paused 500 millisecond...
// Output: 3

DelayQueueExecutor

DelayQueueExecutor calls functions one by one with a delay time period between calls.

If you want this feature but do not want rxjs dependencies, you can have a look on a zero dependencies alternative: [BottleNeck](https://github.com/SGrondin/bottleneck）

Picture Credit: ReactiveX Single Operator Delay

Practical examples of DelayQueueExecutor:

1. We are calling a HTTP API which can only be called no more than ten times per second, or it will throw a 500 error.

Example:

import { DelayQueueExecutor } from 'rx-queue'

const delay = new DelayQueueExecutor(500)  // set delay period time to 500 milliseconds

delay.execute(() => console.log(1))
delay.execute(() => console.log(2))
delay.execute(() => console.log(3))

// Output: 1
// Paused 500 millisecond...
// Output: 2
// Paused 500 millisecond...
// Output: 3

concurrencyExecuter()

When we have a array and need to use an async function to get the result of them, we can use Promise.all():

const asyncTask = async function (item) {
  /**
   * Some heavy task, like:
   *  1. requires XXX MB of memory
   *  2. make 10+ new network connections and each takes 10+ seconds
   *  3. etc.
   */
}

const result = await Promise.all(
  hugeArray.map(item => asyncTask),
)

Because the above example asyncTask requires lots of resource for each task, so if the hugeArray has many items, like 1,000+, then to use the Promise.all will very likely to crash the system.

The solution is that we can use concurrencyExecuter() to execute them in parallel with a concurrency limitation.

// async task:
const heavyTask = (n: number) => Promise.resolve(resolve => setTimeout(resolve(n^2), 100))

const results = concurrencyExecuter(
  2,          // concurrency
)(
  heavyTask,  // task async function
)(
  [1, 2, 3],  // task arguments
)

/**
 * in the following `for` loop, we will have 2 currency tasks running at the same time.
 */
for await (const result of results) {
  console.log(result)
}

That's it.

SEE ALSO

• Writing Marble Tests

CHANGELOG

main v1.0 (Nov 23, 2021)

1. ES Module Support
2. TypeScript 4.5
3. concurrencyExecuter() method added

v0.12 - May 2021

1. Upgrade RxJS to v7.1
2. Upgrade TypeScript to v4.3
3. Fix RxJS breaking changes #71

v0.8 - Mar 2019

1. Fix typo: issue #40 - rename DelayQueueExector to DelayQueueExecutor

v0.6 - Sep 2018

1. fix exception bug in browser(ie. Angular)

v0.4 - May 2018

1. Upgrade to RxJS 6
2. Moved CI from Travis-ci.org to Travis-ci.com

v0.2 - Oct 30, 2017

1. Support: DelayQueue, ThrottleQueue, DebounceQueue, DelayQueueExecutor.
2. first version

AUTHOR

Huan LI (李卓桓) <zixia@zixia.net>

COPYRIGHT & LICENSE

• Code & Docs © 2017-now Huan LI <zixia@zixia.net>
• Code released under the Apache-2.0 License
• Docs released under Creative Commons