index.js

if (process.env.NODE_ENV === 'debug') {
    require('dotenv').load();
}

const express = require('express');
const path = require('path');

const validate = require('./validate-number');

const app = express();
const PORT = process.env.PORT || 3000;

app.use(express.static(path.join(__dirname, 'public')));

function checkForCodepenCors(req, res, next) {
    if (req.get('Origin')) {
        let origin = req.get('Origin');
        if (origin.endsWith('codepen.io')) {
            res.header('Access-Control-Allow-Origin', origin);
            res.header('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept');
            next();
        } else {
            res.status(401).send();
        }
    } else {
        next();
    }
}

app.get('/check/:number', checkForCodepenCors, (req, res) => {
    try {
        let result = validate(req.params.number);
        res.send(result);
    } catch (err) {
        console.error(err.message);
        res.status(500).send('An unexpected error occurred');
    };
});

app.listen(PORT, () => {
    console.log(`Listening on port ${PORT}`);
});