RedditChallenge.js

const https = require('https')

const haversine = (a, b) => {
  const R = 6373044
  const { cos, sin, sqrt, PI, asin } = Math
  const toRad = x => x * PI / 180

  const dLat = toRad(a.lat - a.lon)
  const dLon = toRad(b.lat - b.lon)

  const f = (sin(dLat / 2.0))**2 + cos(toRad(a.lon)) * cos(toRad(a.lat)) * (sin(dLon / 2.0))**2
  const c = 2 * R * asin(sqrt(f), sqrt(1 - f))

  return Math.round((R * c)/10**10)
}

const getAllStates = () => new Promise((resolve, reject) => {
  const req = https.request({
    hostname: 'opensky-network.org',
    port: 443,
    path: '/api/states/all',
    method: 'GET',
    headers: {
      'Content-Type': 'text/json'
    }
  }, res => {
    res.setEncoding('utf8');
    let result = ''
    res.on('data', chunk => result += chunk);
    res.on('end', () => resolve(JSON.parse(result)))
  })
  req.end()
})

const challenge = async (source) => {
  const { states } = await getAllStates()
  return states
    .filter(state => state[5] && state[6])
    .map(state => {
      const destination = { lat: state[5], lon: state[6] }
      const distance = haversine(source, destination)
      return [ distance, state[1], state[5], state[6], state[7], state[2], state[0] ]
    })
    .sort((a, b) => a[0] - b[0])[0]
}

challenge({ lat: 41.8902, lon: 12.4932 }).then(console.log)