ConsumerX

An asynchronous jobs (Promise | Async Function) consumer which can deal with priority based on RxJS, having error-handling and retry mechanism and can specify callback on success and failure. Can be used in browser and node environment.

Quick Start

Install

consumer-x

$ yarn add consumer-x

Overview

Introduction

ConsumerX is a simple asynchronous priority jobs consumer with error-handling and retry mechanism built with TypeScript and RxJS, which can run on Node.JS environment and browser.

Basic Usage

import ConsumerX from 'consumer-x';

const consumer = new ConsumerX(2, 100); // Parameters have default value: retryCount = 0, intervalTime = 200

// promise as job
const testPromiseResolve = () => {
  return new Promise(resolve => {
    resolve('resolve from promise');
  })
}

const testPromiseReject = () => {
  console.log('called!');
  return new Promise((_resolve, reject) => {
    reject('reject from promise');
  })
}

// You can also push async function as job
const testAsync = async() => {
  try {
    const res = await testPromiseResolve();
    return res + '?No, is from async';
  } catch(err) {
    throw Error('error');
  }
}

consumer.push({
  task: testPromiseResolve,
  success: (res) => {
    console.log('Success~~ ', res);
  },
  failure: (err) => {
    console.log('Failure ', err);
  }
}, 3) // second argument is priority

consumer.push({
  task: testPromiseReject,
  success: (res) => {
    console.log('Success ', res);
  },
  failure: (err) => {
    console.log('Failure ', err);
  }
}, 2)

consumer.push({
  task: testAsync,
  success: (res) => {
    console.log('Success!! ', res);
  },
  failure: (err) => {
    console.log('Failure ', err);
  }
}) // If you don't specify the priority, the default value will be 5. 

consumer.push({
  task: testAsync,
  success: (res) => {
    console.log('Success$$ ', res);
  },
  failure: (err) => {
    console.log('Failure ', err);
  }
})

/*
The console will log:

called!
called!
called!
Failure  reject from promise
(Because the testPromiseReject's priority is highest, so it run first, and because we set the retryCount to 2 when we created the instance, so it will retry two time (the initial call + 2 retry count, so totally 3 times.) If the last retry also fail, it will call the failure callback.)

Success~~  resolve from promise

Success!!  resolve from promise?No, is from async
(Default priority is 5, which is the lowest in this case.)

Success$$  resolve from promise?No, is from async
(If tasks have same priority, it will work like normal queue (FIFO).)
*/

Running tests

$ yarn test

Parameters

Param	Type	Description
retryCount	number	The retry count when job encounter failure. (Default Value = 0)
intervalTime	number	The interval delay between each two tasks. (Default Value = 200ms)

Priority Queue

ConsumerX implement a linear data structure priority queue instead of heap based priority to make sure the order of tasks with same priority.(It's relatively difficult to achieve this in heap-based priority queue.)

Method	Big O
push	O(1)
size	O(1)
isEmpty	O(1)
pop	O(n)

Priority

You can specify priority of each task while pushing the task

consumer.push({
  task: testPromise,
  success: (res) => {
    console.log('Success ', res);
  },
  failure: (err) => {
    console.log('Failure ', err);
  }
}, 2);

The lower number has a higher priority than the bigger number, the default priority is 5.

If the tasks have same priorities, it will be implemented with pattern of First In First Out (FIFO).

Defer

Use RxJS defer to achieve lazy execution.

QueueEntity

interface IQueueEntity<Result> {
  task: () => Promise<Result>;
  success?: (res: Result) => void;
  failure?: (err: unknown) => void;
}

currently accept promise and async function as job, will probably support other types in the future.

Roadmap

• [X] Implement priority queue
• [X] Setup lint-stage
• [X] Add Prettier
• [ ] Increase unit test and maintain high testing coverage
• [ ] CI/CD pipeline
• [ ] Take advantage of more RxJS features

License