Express web-server for Angular app with cached HTTP API backend

helpers.js

'use strict';

module.exports.jsonResponseObject = function jsonResponseObject(err, data) {
  return {
    meta: {
      status: err ? (err.status || 500) : 200,
      message: err ? (err.message || 'Error') : 'OK'
    },
    response: data || {}
  };
};

router.js

'use strict';

const express = require('express');
const path = require('path');
const cache = require('memory-cache');
const helpers = require('./helpers');

const router = new express.Router();
const responseObject = helpers.jsonResponseObject;
const cacheTimeout = 15 * 60 * 1000;

// Angular app
router.use('/', express.static(path.join(__dirname, '/static')));

// API calls
router.use('/api/posts', (req, res) => {
  let key = 'test-key';
  let cached = cache.get(key);

  if (!cached) {
    // Add value stating that a fresh data request is pending
    cache.put(key, 'pending', 5000);

    // Get fresh data
    myApi.expensiveOperation((err, data) => {
      if (err) {
        return console.error('api call error', err);
      }
      console.log('Cache key %s updated with fresh data', key);

      // Fill up the cache with the real data
      cache.put(key, data, cacheTimeout);
    });

    // Return empty array
    return res.json(responseObject('Data not ready...'));
  }

  // Return cache data
  return res.json(responseObject(null, cache.get(key)));
});

module.exports = router;

server.js

'use strict';

const express = require('express');
const helmet = require('helmet');
const router = require('./router.js');
const helpers = require('./helpers');
const responseObject = helpers.jsonResponseObject;

const app = express();

app.use(helmet());
app.use(router);

app.use(function errorHandler(err, req, res, next) { // eslint-disable-line no-unused-vars
  if (!err) {
    err = new Error('Not found');
    err.status = 404;
  }
  
  console.error('errorHandler', err);

  res
    .status(err.status || 404)
    .json(responseObject(err));
});

module.exports = app;