koa-router not working with generator

Question

I have been struggling to get koa to respond to requests when I use generators. I wrote a test.js app to demonstrate this.

var koa = require('koa');
var app = new koa();
var Router = require('koa-router');
var router = new Router();

router.get('/', function *(next){
    this.body = "hello world";
    console.log("success")
});

app.use(router.routes())
app.use(router.allowedMethods());

app.listen(3000);
console.log("listening on 3000");

I run the server with node v4.6.1

No errors occur, but when I send the get request, I get Not Found and no console log.

This code works though:

var koa = require('koa');
var app = new koa();
var Router = require('koa-router');
var router = new Router();

router.get('/', function (ctx){
    ctx.body = "hello world";
    console.log("success")
});

app.use(router.routes())
app.use(router.allowedMethods());

app.listen(3000);
console.log("listening on 3000");

Any idea why the generators don't run?

Answer 1

If you're using the @next version of koa and koa-router, you should be using async functions for your middleware instead of generator functions which were meant for Koa v1.

Example:

var koa = require('koa');
var app = new koa();
var Router = require('koa-router');
var router = new Router();

router.get('/', async function (ctx){
    // You can use `await` in here
    ctx.body = "hello world";
    console.log("success")
});

app.use(router.routes())
app.use(router.allowedMethods());

app.listen(3000);
console.log("listening on 3000");

Of course, async/await isn't supported right now unless you're using Node v7 and use the --harmony-async-await flag. If you want to use it with Node v4, you will have to use something like babel in order to transpile your code. If you don't want to have a build step for your server-side code, I would recommend just using Koa v1 and stick with generator functions.