Object no longer instance of Class after adding to Bull queue

Question

In the handler of my Fastify route, I'm adding to my Bull queue an object of a class. In the queue's process method, this object is no longer an instance of the class. Is this normal or am I missing some (or a lot) of the basics?

const fastify = require('fastify')({ logger: true })
const Queue = require('bull');
let addQueue = new Queue('Add', 'redis://127.0.0.1:6379');

...

addQueue.process(function(job, done){
  console.log(job.data.dataObj instanceof ClasssDefinedSomwhereElse);
}

...

fastify.route({
  method: 'POST',
  url: '/',
  ...
  handler: async (request, reply) => {
    if(isFirstRequest) {
      classObj = new ClasssDefinedSomwhereElse();
      isFirstRequest = false;
    } else {
      console.log(classObj instanceof ClasssDefinedSomwhereElse);
      addQueue.add({dataObj: classObj});
    }

addQueue.add({dataObj: classObj}); or addQueue.add(classObj); makes no difference. The handler prints true & the process method prints false. Why is this?

What I'm eventually trying to do is, in the process method, call a method of the class using the object that I've just passed in. I'm not from a Javascript background so I think I might've missed something basic. Any help is appreciated.

Answer 1

In javascript, the class, is not the same as class in Object-Oriented Programming. The class is just syntactic sugar for the prototype

So what is happening in your software is that:

• add a class instance to the bull queue
• bull will serialize the object in redis (depending on the toString() implementation)
• bull will run in async the queue, fetching the string data from redis and parsing it to an object (like running JSON.parse(aJsonString)

In this process, there is no information about the ClasssDefinedSomwhereElse (like it would be in a class serialization in Java). So you need to create a new instance of that class, based on the simple JSON that Bull is fetching.