什么将导出JavaScript/Node.JS文件?

我正在学习NodeJS教程,我看到了下面的代码,我不明白这个模块将导出什么,以及有人将进入什么 cors 当他/她这样做时 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);