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Expressive middleware for node.js using generators
JavaScript Other

Merge pull request #460 from mking/patch-1

Clarify precondition for freshness check
latest commit 69ed37335b
@jonathanong jonathanong authored

koa middleware framework for nodejs

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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.


$ npm install koa

Koa is supported in all versions of iojs without any flags.

To use Koa with node, you must be running node 0.11.16 or higher for generator and promise support, and must run node(1) with the --harmony-generators or --harmony flag.


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.
  • Introduction Screencast - An introduction to installing and getting started with Koa


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';


Running tests

$ make test




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