Is there a way to bootstrap an Express app? - express

Question

I'm building an app in Express but I'd like it to call out to S3 to retrieve some keys before the server actually starts up. Is this possible in Express? If I google bootstrap Express I get hits for setting up Express with twitter Bootstrap.
I have used Sails.js before and you could specify bootstrap configurations in a bootstrap.js file so I guess I'm looking for something similar. Otherwise are there alternatives?
I have a index.js file and a separate bin/www file which calls the index.js file. I'd like the bootstrapping done in index.js so that it's included as part of the tests. Right now I 'initialize' the bootstrap but as it's asynchronous the server is already up and running before the bootstrap has complete (or errored out) i.e.
import express from 'express';
import {initializeFromS3} from './services/initializerService';
import healthCheckRouter from './routes/healthCheckRouter';
import bodyParser from 'body-parser';
initializeFromS3(); // Calls out to S3 and does some bootstrapping of configurations
const app = express();
app.use(bodyParser.json()); // to support JSON-encoded bodies
app.use(bodyParser.urlencoded({ // to support URL-encoded bodies
extended: true
}));
// ---------------------------- Routes ----------------------------
app.use('/', express.static('dist/client/'));
app.use('/health-check', healthCheckRouter);
export default app;

Answer 1

Posting my solution for anyone who comes across the same and has a mind blank. I kept the bin/www and index.js files separately but had the express object returned from index.js via a method. Solution below thanks to the friendly people of Github.
Index.js file:
import express from 'express';
import {initialize} from './services/appService';
import healthCheckRouter from './routes/healthCheckRouter';
import loginRouter from './routes/loginRouter';
export function getExpress() {
return initialize()
.then(() => {
const app = express();
// ---------------------------- Routes ----------------------------
app.use('/', express.static('dist/client/'));
app.use('/login', loginRouter);
app.use('/health-check', healthCheckRouter);
return app;
})
}
bin/www file:
import winston from 'winston';
import bodyParser from 'body-parser';
import {getExpress} from '../index';
getExpress()
.then(app => {
app.use(bodyParser.json()); // to support JSON-encoded bodies
app.use(bodyParser.urlencoded({ // to support URL-encoded bodies
extended: true
}));
const port = 3002;
app.listen(port, () => {
winston.info(`Server listening on port ${port}!`);
});
})
.catch(err => {
winston.error('Error starting server', err);
});
Integration tests:
import request from 'supertest';
import {getExpress} from '../../index'
describe('/login integration test', () => {
let app = null;
beforeEach(done => {
getExpress()
.then(res => {
app = res;
done();
});
});
describe('GET /login', () => {
it('should return 400 error if \'app\' is not provided as a query string', done => {
request(app)
.get('/login')
.expect(400, done);
});
});
});