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