server.js

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

// init project
var express = require("express");
var app = express();
var api_route = require("./routes");

// 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({ optionSuccessStatus: 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/timestamp/:date_string?", (req, res) => {
  let date_string = req.params.date_string;
  let date = null;

  if (!date_string) {
    date = new Date();
  } else {
     date = new Date(date_string);
  }

  if (/\d{5,}/.test(date_string)) {
    dateInt = parseInt(date_string);
    //Date regards numbers as unix timestamps, strings are processed differently
    res.json({ unix: date_string, utc: new Date(dateInt).toUTCString() });
  }

  if (date.getTime()) {
    res.json({ unix: date.getTime(), utc: date.toUTCString() });
  } else {
    res.json({ error: "Invalid Date" });
  }
});
// listen for requests :)
var listener = app.listen(process.env.PORT, function() {
  console.log("Your app is listening on port " + listener.address().port);
});