index.js

// index.js
// where your node app starts

// init project
var express = require('express');
var app = express();

// enable CORS (https://en.wikipedia.org/wiki/Cross-origin_resource_sharing)
// so that your API is remotely testable by FCC 
var cors = require('cors');
app.use(cors({optionsSuccessStatus: 200}));  // some legacy browsers choke on 204

// http://expressjs.com/en/starter/static-files.html
app.use(express.static('public'));

// http://expressjs.com/en/starter/basic-routing.html
app.get("/", function (req, res) {
  res.sendFile(__dirname + '/views/index.html');
});


// your first API endpoint... 
app.get("/api/hello", function (req, res) {
  res.json({greeting: 'hello API'});
});

app.get("/api/:date?", function(req, res) {
  let dateParam = req.params.date;
  let output;

  if (!isNaN(Number(dateParam))) {
    dateParam = Number(dateParam);
  }

  if (!dateParam) {
    output = new Date();
  } else if (isValidDate(dateParam)) {
    output = new Date(dateParam);
  } else {
    res.json({ error : "Invalid Date" });
    return;
  }

  res.json({
    unix: output.getTime(),
    utc: output.toUTCString()
  })

  function isValidDate(MaybeUnixNum) {
    let date = new Date(MaybeUnixNum);
    return !isNaN(date.getTime());
  }
});

// Listen on port set in environment variable or default to 3000
var listener = app.listen(process.env.PORT || 3000, function () {
  console.log('Your app is listening on port ' + listener.address().port);
});