job-queue.js

const Queue = require('bull');

const pdfQueue = new Queue('pdf', 'redis://localhost:6379');

const delay = (milliseconds) =>
  new Promise((resolve) => setTimeout(resolve, milliseconds));

const CONCURRENCY = 2;

pdfQueue.process(CONCURRENCY, async function (job) {
  console.log(`creating pdf ${job.data.fileName}... `);
  await delay(2000);
  console.log(`pdf ${job.data.fileName} created`);
});

pdfQueue.add({ fileName: 'example1.pdf' });
pdfQueue.add({ fileName: 'example2.pdf' });
pdfQueue.add({ fileName: 'example3.pdf' });
pdfQueue.add({ fileName: 'example4.pdf' });


// output 👇
/*
creating pdf example1.pdf... 
creating pdf example2.pdf... 
pdf example1.pdf created
pdf example2.pdf created
creating pdf example3.pdf... 
creating pdf example4.pdf... 
pdf example3.pdf created
pdf example4.pdf created
*/