NodeJs Require module returns an empty object

Question

I'm using NodeJS 8 LTS.

I have 3 js scripts where:

// main.js
const dom = require ('./Domains/Domains');
const factory = require ('./Domains/Factory');
(async () => {
    const Domain = await factory.foo();  // <=== Error

})();

// Domains.js
class Domains {
    constructor (options = {}) {
        ....
    }
}
module.exports = Domains;

// Factory.js
const Domains = require('./Domains');
module.exports = {
   foo: async () =>{

      .... async stuff ...

     return new Domains();
    }
};

when I run main.js I get

(node:1816) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): TypeError: Domains is not a constructor
warning.js:18
(node:1816) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Debugging, I found that in Factory.js when it requires Domanis.js const Domains = require('./Domains'); it returns an empty object.

Looking around on internet I found that it happens when there are a circular dependencies between modules (Require returns an empty object) but It doesn't seem the case here.

Any idea?

In short: Node creates empty objects when circular dependencies occurs. Then you have to find a way out by getting the dependency dynamically or something else. Also, you can detect circular dependencies with an npm package called madge, with npx madge --circular <app entry point> Here's a video that could help: youtube.com/watch?v=JQQX62cUaYw — tkpb
– tkpb, Commented Feb 13, 2022 at 11:51

Gappa · Accepted Answer · 2018-09-19 12:25:29Z

11

Finally, I got the the issue's origin. The empty object was due to a circular dependency derived by another require that was inside Domains.js

// Domains.js
const another_module= require("circular_dep_creator");
class Domains {
    constructor (options = {}) {
        ....
    }
}
module.exports = Domains;

// circular_dep_creator.js
const factory = require ('./Domains/Factory');
...
another stuff

So, this causes a circular dependency that creates an empty object

answered Sep 19, 2018 at 12:25

Gappa

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1 Comment

Lucas Fabre Over a year ago

A good module to find circular dependencies is Medge. Install to your Dev Dependencies and run as npx medge --circular <EntryFile> npmjs.com/package/madge

Mykrosoft · Accepted Answer · 2020-01-23 09:30:18Z

-4

The setImmediate call will delay the loading of the required module until the browser has finished doing what it needs to do. This may cause some issues where you try to use this module before it is loaded, but you could add checks for that.

// produces an empty object
const module = require('./someModule');

// produces the required object
let module;
setImmediate(() => {
  module = required('./someModule');
});

edited Jan 23, 2020 at 9:30

Mykrosoft

51 silver badge4 bronze badges

answered Aug 20, 2019 at 16:02

Vitaliy Trots

11 bronze badge

1 Comment

tkpb Over a year ago

Everything wrong (...browser, delay). At least you give the clue for the setImmediate function that could help in some cases.

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