# aldo-application

> Aldo's application package

Latest version **1.0.0-alpha.0** (published 2018-05-22) · MIT license · 0 weekly downloads

## Install

```sh
npm install aldo-application
pnpm add aldo-application
yarn add aldo-application
bun add aldo-application
```

## Health

**Score 25/100 (F)** — status: abandoned.

Positive: has types; no vulnerabilities; high quality score.

Warnings: low downloads; no esm support.

Negative: abandoned; low maintenance score.

## Facts

| | |
|---|---|
| Version | 1.0.0-alpha.0 |
| Published | 2018-05-22 |
| First published | 2018-05-22 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | bundled |
| Module format | CommonJS |
| Node | >=8.9 |
| Dependencies | 5 |
| Unpacked size | 9.8 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| GitHub stars | 0 |
| Author | absolux |
| Maintainers | absolux |
| Keywords | aldo, middleware, dispatcher, application |

## Links

- npm: https://www.npmjs.com/package/aldo-application
- Repository: https://github.com/aldojs/aldo
- Homepage: https://github.com/aldojs/application#readme
- Issues: https://github.com/aldojs/application/issues
- npm.io page: https://npm.io/package/aldo-application

## Dependencies (5)

- [debug](https://npm.io/package/debug.md) ^3.1.0
- [aldo-http](https://npm.io/package/aldo-http.md) ^1.0.0-alpha.2
- [aldo-compose](https://npm.io/package/aldo-compose.md) ^3.1.2
- [aldo-context](https://npm.io/package/aldo-context.md) ^1.1.1
- [@sindresorhus/is](https://npm.io/package/@sindresorhus/is.md) ^0.9.0

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## Recent versions

- 1.0.0-alpha.0 (latest) — 2018-05-22

## README

`Aldo-application` is an object containing a stack of [middleware](#middlewares) functions which are composed and executed upon each HTTP request.

```js
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](#context) and a `next` function to call the downstream middlewares, and must return a [response](#response) as output.

```ts
// 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)`

```js
// 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

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

  return next()
})
```

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

```js
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)`

```ts
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)`

```js
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.

```js
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`

---
_Source: https://npm.io/package/aldo-application · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._