koa-mount

What is koa-mount?

The `koa-mount` package is a middleware for the Koa framework that allows you to mount other Koa applications or middleware at specific paths. This is useful for structuring your application into smaller, more manageable pieces or for integrating third-party applications.

What are koa-mount's main functionalities?

Mounting a Koa application at a specific path

This feature allows you to mount a sub-application at a specific path. In this example, requests to `/sub` will be handled by `subApp`.

const Koa = require('koa');
const mount = require('koa-mount');

const app = new Koa();
const subApp = new Koa();

subApp.use(async (ctx) => {
  ctx.body = 'Hello from subApp!';
});

app.use(mount('/sub', subApp));

app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});

Mounting middleware at a specific path

This feature allows you to mount specific middleware at a given path. In this example, requests to `/middleware` will be handled by the `middleware` function.

const Koa = require('koa');
const mount = require('koa-mount');

const app = new Koa();

const middleware = async (ctx, next) => {
  ctx.body = 'Hello from middleware!';
  await next();
};

app.use(mount('/middleware', middleware));

app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});

Other packages similar to koa-mount

koa-router

The `koa-router` package provides a powerful routing solution for Koa applications. It allows you to define routes and their handlers, including support for nested routes and middleware. Unlike `koa-mount`, which is focused on mounting entire applications or middleware at specific paths, `koa-router` is more focused on defining and handling individual routes.

express

While not a Koa-specific package, `express` is a popular web framework for Node.js that includes built-in support for routing and middleware. It offers similar functionality to `koa-mount` in terms of mounting sub-applications and middleware, but it is designed for use with the Express framework rather than Koa.

README

koa-mount

Mount other Koa applications as middleware. The path passed to mount() is stripped from the URL temporarily until the stack unwinds. This is useful for creating entire apps or middleware that will function correctly regardless of which path segment(s) they should operate on.

Installation

$ npm install koa-mount

Examples

View the ./examples directory for working examples.

Mounting Applications

Entire applications mounted at specific paths. For example you could mount a blog application at "/blog", with a router that matches paths such as "GET /", "GET /posts", and will behave properly for "GET /blog/posts" etc when mounted.

const mount = require('koa-mount');
const Koa = require('koa');

// hello

const a = new Koa();

a.use(async function (ctx, next){
  await next();
  ctx.body = 'Hello';
});

// world

const b = new Koa();

b.use(async function (ctx, next){
  await next();
  ctx.body = 'World';
});

// app

const app = new Koa();

app.use(mount('/hello', a));
app.use(mount('/world', b));

app.listen(3000);
console.log('listening on port 3000');

Try the following requests:

$ GET /
Not Found

$ GET /hello
Hello

$ GET /world
World

Mounting Middleware

Mount middleware at specific paths, allowing them to operate independently of the prefix, as they're not aware of it.

const mount = require('koa-mount');
const Koa = require('koa');

async function hello(ctx, next){
  await next();
  ctx.body = 'Hello';
}

async function world(ctx, next){
  await next();
  ctx.body = 'World';
}

const app = new Koa();

app.use(mount('/hello', hello));
app.use(mount('/world', world));

app.listen(3000);
console.log('listening on port 3000');

Optional Paths

The path argument is optional, defaulting to "/":

app.use(mount(a));
app.use(mount(b));

Debugging

Use the DEBUG environement variable to whitelist koa-mount debug output:

$ DEBUG=koa-mount node myapp.js &
$ GET /foo/bar/baz

  koa-mount enter /foo/bar/baz -> /bar/baz +2s
  koa-mount enter /bar/baz -> /baz +0ms
  koa-mount enter /baz -> / +0ms
  koa-mount leave /baz -> / +1ms
  koa-mount leave /bar/baz -> /baz +0ms
  koa-mount leave /foo/bar/baz -> /bar/baz +0ms

License

MIT