Added Koa example (#800)

* Added Koa example

* Linted koa example

README.md

@@ -356,6 +356,7 @@ export default ({ url }) => (
   <ul>
     <li><a href="./examples/custom-server">Basic custom server</a></li>
     <li><a href="./examples/custom-server-express">Express integration</a></li>
+    <li><a href="./examples/custom-server-koa">Koa integration</a></li>
     <li><a href="./examples/parameterized-routing">Parameterized routing</a></li>
     <li><a href="./examples/ssr-caching">SSR caching</a></li>
   </ul>

examples/custom-server-koa/README.md

@@ -0,0 +1,32 @@
+
+# Custom Koa Server example
+
+## How to use
+
+Download the example [or clone the repo](https://github.com/zeit/next.js):
+
+```bash
+curl https://codeload.github.com/zeit/next.js/tar.gz/master | tar -xz --strip=2 next.js-master/examples/custom-server-koa
+cd custom-server-koa
+```
+
+Install it and run:
+
+```bash
+npm install
+npm run dev
+```
+
+Deploy it to the cloud with [now](https://zeit.co/now) ([download](https://zeit.co/download))
+
+```bash
+now
+```
+
+## The idea behind the example
+
+Most of the times the default Next server will be enough but sometimes you want to run your own server to customize routes or other kind of the app behavior. Next provides a [Custom server and routing](https://github.com/zeit/next.js#custom-server-and-routing) so you can customize as much as you want.
+
+Because the Next.js server is just a node.js module you can combine it with any other part of the node.js ecosystem. in this case we are using [Koa](http://koajs.com/) to build a custom router on top of Next.
+
+The example shows a server that serves the component living in `pages/a.js` when the route `/b` is requested and `pages/b.js` when the route `/a` is accessed. This is obviously a non-standard routing strategy. You can see how this custom routing is being made inside `server.js`.

examples/custom-server-koa/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "custom-server-koa",
+  "scripts": {
+    "dev": "node server.js",
+    "build": "next build",
+    "start": "NODE_ENV=production node server.js"
+  },
+  "dependencies": {
+    "koa": "^1.2.4",
+    "koa-router": "^5.4.0",
+    "next": "^2.0.0-beta"
+  }
+}

examples/custom-server-koa/pages/a.js

@@ -0,0 +1 @@
+export default () => <div>a</div>

examples/custom-server-koa/pages/b.js

@@ -0,0 +1 @@
+export default () => <div>b</div>

examples/custom-server-koa/pages/index.js

@@ -0,0 +1,9 @@
+import React from 'react'
+import Link from 'next/link'
+
+export default () => (
+  <ul>
+    <li><Link href='/b' as='/a'><a>a</a></Link></li>
+    <li><Link href='/a' as='/b'><a>b</a></Link></li>
+  </ul>
+)

examples/custom-server-koa/server.js

@@ -0,0 +1,34 @@
+const Koa = require('koa')
+const next = require('next')
+const Router = require('koa-router')
+
+const dev = process.env.NODE_ENV !== 'production'
+const app = next({ dev })
+const handle = app.getRequestHandler()
+
+app.prepare()
+.then(() => {
+  const server = new Koa()
+  const router = new Router()
+
+  router.get('/a', function *() {
+    app.render(this.req, this.res, '/b', this.query)
+    this.respond = false
+  })
+
+  router.get('/b', function *() {
+    app.render(this.req, this.res, '/a', this.query)
+    this.respond = false
+  })
+
+  router.get('*', function *() {
+    handle(this.req, this.res)
+    this.respond = false
+  })
+
+  server.use(router.routes())
+  server.listen(3000, (err) => {
+    if (err) throw err
+    console.log('> Ready on http://localhost:3000')
+  })
+})