NodeJS 导出类无法读取未定义的属性

Question

I am currently trying to add a service layer to my NodeJS project, which is a simple API I build using express and sequelize. The project has a structure of the usual model, route, and controller (MRC) form; each has its own directory. Now all I need to do is add another directory that will contain the service files. The files will contain the business logic in the form of a class that I will export and include in my controller files.

Here I will display the controller and service files:

eruptionController.js

const EruptionService = require('../services/eruptionService.js');
let Eruption = new EruptionService()


module.exports = {
    getEruptions: (req, res) => {
        Eruption.get().then(result => {
            return res.status(200).json({
                message: "Get All Eruptions",
                result
            })
        }).catch(err => {
            return res.status(200).json({
                message: "internal Server Error",
                error: err.message
            })
        })
    }
};

eruptionService.js

const { eruption } = require('../models');

class EruptionService {
    constructor () {
        this.eruptionModel = eruption;
        
    }

    get () {
        this.eruptionModel.findAll()
        .then(result => result)
        .catch(err => err)
    }
}

module.exports = EruptionService;

As we can see here, in the service file, I imported the eruption model from the model folder and include it in the constructor. Then I created a method named get , which purpose to retrieve all the eruption data from the database.

After that, I imported the EruptionService class into the controller file, initiated it as an instance, and include the class in the getEruptions function. The function will then be used in an express route in the form of an endpoint.

The issue is that when I tried to send a request to the endpoint, I got the following error

TypeError: Cannot read property 'then' of undefined

Based on the error, it seems that the EruptionService class was not exported properly since when I called the mothed get it's undefined.

I've been stuck with this for a while now, and I'm not really sure what's going on. Based on this post , I seem to be exporting the class properly.

I've also tried exporting in a way like below

module.exports = {EruptionService: EruptionService}

And I've also tried importing like

const EruptionService = require('../services/eruptionService.js');

But in the end, it either results in the same error or different one kind of error. I was wondering if anybody could point out what I was missing? Thanks in advance

Answer 1

You should return a promise function for getting the then function inside it. There is a issue in your service it should be like the below snippet

 class EruptionService {
    constructor () {
        this.eruptionModel = eruption;
        
    }

    get () {
        return this.eruptionModel.findAll()
    }
}