[](https://travis-ci.org/koajs/koa) Expressive middleware for node.js using generators via [co](https://github.com/visionmedia/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 ~400 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](https://github.com/koajs/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' ``` Another option, if you would like to use koa with __node 0.10.x__ (the current stable branch), or are tired of typing the `--harmony` flag, is to use [`gnode`](https://github.com/TooTallNate/gnode) to spawn your node instance. However note that performance degrades quickly compared to 0.11.x. ## Community - [API](docs/api/index.md) documentation - [Examples](https://github.com/koajs/examples) - [Middleware](https://github.com/koajs/koa/wiki) list - [Wiki](https://github.com/koajs/koa/wiki) - [G+ Community](https://plus.google.com/communities/101845768320796750641) - [Mailing list](https://groups.google.com/forum/#!forum/koajs) - [Guide](docs/guide.md) - [FAQ](docs/faq.md) - __#koajs__ on freenode ## Example ```js 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); ``` ## Running tests ``` $ make test ``` ## Benchmarks If you like silly benchmarks, here's the requests per second using [wrk](https://github.com/wg/wrk) 3.x on my MBP. ``` 1 middleware 8367.03 5 middleware 8074.10 10 middleware 7526.55 15 middleware 7399.92 20 middleware 7055.33 30 middleware 6460.17 50 middleware 5671.98 100 middleware 4349.37 ``` With __50__ middleware (likely much more than you'll need), that's __340,260__ requests per minute, and __20,415,600__ per hour, and over __440 million__ per day, so unless you're a Facebook and can't manage to spin up more than one process to scale horizontally you'll be fine ;) ## Authors - [TJ Holowaychuk](https://github.com/visionmedia) - [Jonathan Ong](https://github.com/jonathanong) - [Julian Gruber](https://github.com/juliangruber) # License MIT