Why is a function provided by require undefined in a class instance?

Question

I'm asking this mostly as a sanity check, I'm unsure if I have made a mistake somewhere or if this fundamentally does not work.

I am converting some Java to Nodejs, A class called Site populates itself from a database via the dataFunctions.getSiteInfo(id) function. It also stores a list of Page instances.

The issue is that dataFunctions is returning as undefined when an instance of Site is created.

Have I misunderstood how classes and modules work in this case? Is it possible for instances of this class to access the dataFunctions module? Likewise is it possible for the Site class to reference the Page class as well? Or have I made some other silly mistake?

Site.js

let Page = require('./Page.js');
let dataFunctions = require('../DataFunctions.js');

module.exports = class Site {
    constructor(id) {
        this.id = id;
        this.pages = [];

        console.log(dataFunctions);
        this.siteInfo = dataFunctions.getSiteInfo(id);

DataFunctions.js

let Site = require('./classes/Site.js');

function makeASite() {
    let id = 2;
    let site = new Site(id);
}

function getSiteInfo(id) {
    etc etc
}

module.exports = {
    getSiteInfo: function (id) {
        return getSiteInfo(id);
    },
};

Answer 1

Based on the code provided, I believe you forgot to create a new dataFunctions instance.

const df = new dataFunctions();
console.log(df);

If dataFunctions is providing static functions, make sure that the getSiteInfo method is static.

Otherwise, additional details may be needed.

Edit

It looked like the project structure and the require paths were wonky, but it's hard to tell.

When I run the code provided using the project structure inferred by the require statements, I'm not able to reproduce your issue.

However, one problem that I do see is that you're requiring the Site.js module from the DataFunctions.js module and requiring the DataFunctions.js module from the Site.js module, creating circular dependencies. Try eliminating these by moving makeASite to the Site.js module, for instance.