Koa web app framework

npm install koa
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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. If you prefer to only define a single dependency for common middleware, much like Connect, you may use koa-common.


$ 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'



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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