Promise Qu

Promise Qu uses recursion to sequentially execute an array of Promises. The queue will wait until the current Promise is resolved before moving on to the next item.

To install

https://www.npmjs.com/package/promise-qu

Why use Promise Qu?

If you have an array of Promises that need to wait for the previous one to resolve before continuing.

Usage

In order to set up a basic queue you can use the following code snippet. In the example below a new queue instance is created and Promise jobs are pushed to the queue. Although there is a setTimeout in the first job, it will wait for this to finish before moving on to job-2 and job-3.

add(() => ...) will push a Promise to the queue.

start() will begin the execution of each job in the queue, this returns a Promise.

const PromiseQu = require('./src');

const isQueueStoppedByError = false;
const q = new PromiseQu(isQueueStoppedByError);

q.add('job-1', () => new Promise((resolve, reject) => {
    setTimeout(() => {
        reject(1);
    }, 1000);
}));

q.add('job-2', () => new Promise((resolve, reject) => {
    resolve(2);
}));

q.add('job-3', () => new Promise((resolve, reject) => {
    resolve(3);
}));

q.start()
    .then(res => console.log(res))
    .catch(error => console.log('ERROR IN QUEUE', error));

Each job has the following structure:

{
    "key": "job-1",
    "job": "<YOUR_FUNCTION>",
    "status": "<ERROR | NOT_STARTED | PENDING | SUCCESS>"
}

The flag isQueueStoppedByError will stop the Queue from continuing to execute if it is set to true. If false it will continue on and push the error to an errors array to view once everything is complete. The end response will look like:

{
    "errors": [
        {
            "result": 1,
            "key": "job-1",
            "status": "ERROR"
        }
    ],
    "success": [
        {
            "key": "job-2",
            "result": 2,
            "status": "SUCCESS"
        },
        {
            "key": "job-3",
            "result": 3,
            "status": "SUCCESS"
        }
    ]
}