api_server.js

const express = require('express');
const fs = require('fs');
const cors = require('cors');
const _ = require('lodash');

const PORT = process.env.PORT || 5000;

const buffer = fs.readFileSync('./data.json');
const { flights } = JSON.parse(buffer);
const carriers = _.uniq(flights.map(flight => flight.carrier));

const app = express();

app.use(cors());

app.get('/', (req, res) => res.send('Hello World!'));

app.get('/carriers', (req, res) => {
  res.json(carriers);
});

app.get('/flights', (req, res) => {
  if (req.query.hasOwnProperty('carriers')) {
    if (req.query['carriers'].length === 0) {
      res.json(flights);
      return;
    }

    const providedCarriers = req.query['carriers']
      .split(',')
      .map(str => _.trim(str));

    const result = flights.filter(flight =>
      providedCarriers.includes(flight.carrier),
    );

    res.json(result);
  } else {
    res.json(flights);
  }
});

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