Tacking shit onto koa context

app.js

var koa = require('koa');
var uuid = require('node-uuid');
var app = koa();

app.use(function *(next) {
  yield next;
  this.log('yippie');
  this.body = 'yoyoyo';
});

app.use(function *() {
  this.id = uuid.v4();
  this.log = function(msg) {
    console.log('id=%s, message=%s', this.id, msg);
  };
});

app.listen(3000);