What will export a JavaScript/Node.JS file?

Question

I am following a NodeJS tutorial that I saw the following code, that I can't understand what will this module export and what will someone get in cors when he/she does var cors = require('./cors') ?

const express = require('express');
const cors = require('cors');
const app = express();

const whitelist = ['http://localhost:3000', 'https://localhost:3443'];
var corsOptionsDelegate = (req, callback) => {
    var corsOptions;
    console.log(req.header('Origin'));
    if(whitelist.indexOf(req.header('Origin')) !== -1) {
        corsOptions = { origin: true };
    }
    else {
        corsOptions = { origin: false };
    }
    callback(null, corsOptions);
};

exports.cors = cors();
exports.corsWithOptions = cors(corsOptionsDelegate);

Answer 1

Node.js file exports the exports object. In this example, this object will consist of two fields: cors and corsWithOptions , with their respective values as were in their assignments.

I assume that your question refers to the situation where this file is saved as cors.js . So a file which imports this file via var cors = require('./cors') would actually assign that same exports object into the cors variable.

To illustrate, if this would be the code in the importing file:

var cors = require('./cors');
console.log(cors)

Then this will be its output:

{ cors: [Function: corsMiddleware],
  corsWithOptions: [Function: corsMiddleware] }