aldo-application

Aldo-application is an object containing a stack of middleware functions which are composed and executed upon each HTTP request.

const { Application } = require('aldo')

const app = new Application()

// add a request handler
app.use(() => 'Hello world!')

// create a HTTP server to serve the application
app.start(process.env.PORT)

Middlewares

Middlewares could be a common or an async function. Each function receives a request context and a next function to call the downstream middlewares, and must return a response as output.

// Handler function signature
declare type Middleware = (ctx: Context, next: () => any) => any;

You can register as many middlewares as needed with the application's method .use(fn)

// to add a handler directly in the stack
app.use(middleware)

Whether a middleware runs before or after a downstream middlewares depends on the middleware itself. For example, the following middleware would perform some task before the others

app.use((ctx, next) => {
  // Perform task

  return next()
})

However, this middleware would perform its task after the request is handled by the following middlewares

app.use(async (ctx, next) => {
  let response = await next()

  // Perform task

  return response
})

Context

The context object is a simple plain object with these properties:

request refers to the incoming request object
response function to get a new Response instance each time called
Other fields defined with .set(key, value) or .bind(key, getter)

declare interface Context {
  request: Request;
  response: ResponseFactory;
  [key: string]: any;
}

To extend the request context, and add shared properties, like a DB connection or a global logger, you may use .set(key, value)

const mongoose = require('mongoose')

await mongoose.connect('mongodb://localhost/test')

app.set('db', mongoose)

To set a per request private properties, you may use .bind(key, getter). This method takes a field name, and a function to be used as a lazy getter of the field value.

app.bind('session', () => new Session(options))

This method is very useful, since it allows you to lazily (only when needed) attach a per request property into the context without adding a dedicated handler.

.has(key) and .get(key) are aldo available to check the existence of a certain field or to get a previously defined field value.

Response

The middleware output could be:

strings or buffers sent directly
streams which will be piped to the outgoing response
null or undefind as empty responses (By default with 204 status code)
Response instances which can be created with the context response property
otherwise, any other value will be serialized as JSON, with the proper Content-Type and Content-Length