Unable to import javascript class. TypeError: "class" is not a constructor

Question

I'm having a really weird issue with importing my class into another module. In my start.js file, I can import the worker module and it runs the script fine. However, when it gets to the socket module and tries to import the worker module, I get the following error.

When I console log worker in the socket.js constructor, it shows as an empty object. When I console log it in the start.js, it shows as a function.

I know this has to be something very simple that I'm overlooking, but I just can't see it.

this.Worker = new worker()
             ^
TypeError: worker is not a constructor
    at new Socket (C:\Users\***\Desktop\***\src\modules\socket.js:7:17)
    at new Worker (C:\Users\***\Desktop\***\src\modules\worker.js:6:17)
    at Object.<anonymous> (C:\Users\***\Desktop\***\start.js:2:16)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Function.Module.runMain (module.js:693:10)
    at startup (bootstrap_node.js:188:16)

I have a start.js file where I import my worker module and start my app.

const worker = require('./src/modules/worker')
const Worker = new worker()

Worker.start()

The worker module (worker.js) imports my socket server module and connects to the socket server.

const socket = require('./socket')

class Worker {

    constructor() {
        this.Socket = new socket()
    }

    async start() {

        try {

            console.log('ran start')
            // Connect to socket server
            await this.Socket.connect()

        } catch(err) {
            console.log('Unable to connect to socket server.', err)
        }
    }

    startJob(work) {
        const jobType = work.work.jobType
        const jobData = work.work.jobData

        // run module based on jobType
    }
}

module.exports = Worker

My socket server module (socket.js) also imports (worker.js) so that I can use the startJob function within the socket.on('process') event as Worker.startJob().

const worker = require('./worker');

class Socket {

    constructor() {
        this.socket = require('socket.io-client')('http://localhost:3000')
        this.Worker = new worker()
    }

    async connect() {

        try {

            // Connect to socket server
            await this.connectServer()

        } catch(err) {
            console.log('Unable to start worker.', err)
        }
    }

    async connectServer() {
        let workerId;

        try {

            // Connection to socket server established
            this.socket.on('connect', () => console.log('Connected to socket server.'))

            // Get socketId for job issuance
            this.socket.on('id', id => { workerId = id })

            // Receive new work orders
            this.socket.on('process', async work => {
                const myId = work.id

                // Check if job was assigned to my socketId
                if (myId == workerId) {
                    console.log('starting job')
                    // await this.Worker.startJob(work)
                }
            })

        } catch(err) {
            console.log('Unable to connect to socket server.', err)
        }
    }
}

module.exports = Socket

1565986223 · Accepted Answer · 2019-04-09 02:48:37Z

4

There are couple of things to note with modules and using export/import

The module.exports object is created by the Module system

So when you do, module.exports = Worker, Worker is added to the module.export object meaning it's a key in the object.

Where you require in your code:

const worker = require('./src/modules/worker')
// class Worker is available as a member
const Worker = new worker.Worker()

If you don't want this, there's two other way you could do:

Destructuring assignment

// note the curly braces and capitalized W because JavaScript is case sensitive
const { Worker } = require('./src/modules/worker');

Or you can replace module.exports with your class this way:

module.exports = class {

  constructor() {
    this.Socket = new socket()
  }

  async start() {

    try {

      console.log('ran start')
      // Connect to socket server
      await this.Socket.connect()

    } catch(err) {
      console.log('Unable to connect to socket server.', err)
    }
  }

  startJob(work) {
    const jobType = work.work.jobType
    const jobData = work.work.jobData

    // run module based on jobType
    }
}

And import like: (Note, You can name it to anything else)

const Worker = require('./worker')

edited Apr 9, 2019 at 2:48

answered Apr 9, 2019 at 2:35

1565986223

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1 Comment

Jayson H Over a year ago

Exactly what I was looking for, thank you for the detailed reply!

Nir Alfasi · Accepted Answer · 2019-04-09 00:15:29Z

0

The error is triggered because you don't have a worker class you have a Worker class (it's case-sensitive).

answered Apr 9, 2019 at 0:15

Nir Alfasi

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1 Comment

Jayson H Over a year ago

I'm importing it as const worker though and setting this.Worker = new worker(). Just like I did in start.js. const worker = require('...'), this.Worker = new worker()

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