koa's Introduction

Expressive middleware for node.js using generators via co to make web applications and APIs more enjoyable to write. Koa's middleware flow in a stack-like manner allowing you to perform actions downstream, then filter and manipulate the response upstream. Koa's use of generators also greatly increases the readability and robustness of your application.

Only methods that are common to nearly all HTTP servers are integrated directly into Koa's small ~550 SLOC codebase. This includes things like content-negotiation, normalization of node inconsistencies, redirection, and a few others.

No middleware are bundled with koa. If you prefer to only define a single dependency for common middleware, much like Connect, you may use koa-common.

Installation

$ npm install koa

To use Koa you must be running node 0.11.9 or higher for generator support, and must run node(1) with the --harmony flag. If you don't like typing this, add an alias to your shell profile:

alias node='node --harmony'

Community

API documentation
Badgeboard and list of official modules
Examples
Middleware list
Wiki
G+ Community
Reddit Community
Mailing list
Guide
FAQ
中文文档
#koajs on freenode

Getting started

kick-off-koa - An intro to koa via a set of self-guided workshops.
workshop - A workshop to learn the basics of koa, Express' spiritual successor.

Example

var koa = require('koa');
var app = koa();

// logger

app.use(function *(next){
  var start = new Date;
  yield next;
  var ms = new Date - start;
  console.log('%s %s - %s', this.method, this.url, ms);
});

// response

app.use(function *(){
  this.body = 'Hello World';
});

app.listen(3000);