server.js

// When your server receives a request on
// http://localhost:4000/set?somekey=somevalue
// it should store the passed key and value in memory.
// When it receives a request on
// http://localhost:4000/get?key=somekey
// it should return the value stored at somekey.

var express = require('express');
var app = express();
var server = require('http').createServer(app);
var port = 4000;
server.listen(4000);

var fs = require('fs');
var database = {};

//in case server shuts down or something
try {
  database = JSON.parse(fs.readFileSync('database.json').toString());
} catch (e) {
  console.log('no database yet');
}

app.get('/', function (req, res) {
  res.send('hello world');
});

app.get('/set', function (req, res, next) {
  var logs = [];
  for (var key in req.query) {
    //database[key] the key is a variable holding some value
    //database.key  the key is literarily key, you put a key property to database :(
    database[key] = req.query[key];
    //console.log(key, req.query[key]);
    logs.push('data saved as: { ' + key + ':' + req.query[key] + '}');
  }
  fs.writeFile('database.json', JSON.stringify(database), function (err) {
    if (err) return next(err);
    console.log('saved data to file');
    res.end(logs.join('\n'));
  });
});

app.get('/get', function (req, res, next) {

  //read file
  fs.readFile('database.json', function (err, data) {
    if (err) return next(err);
    var data;
    try {
      data = JSON.parse(data.toString());
      if (data[req.query.key] !== undefined) {
        res.send(database[req.query.key]);
      } else {
        res.send('ooops no such record :(');
      }
    } catch (e) {
      return next(e);
    }
  });

  // just read from memory
  // if (database[req.query.key] !== undefined) {
  //   res.send(database[req.query.key]);
  // } else {
  //   res.send('ooops no such record :(');
  // }
})