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< img src = "https://dl.dropboxusercontent.com/u/6396913/koa/logo.png" alt = "koa middleware framework for nodejs" width = "255px" / >
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[![gitter][gitter-image]][gitter-url]
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[![NPM version][npm-image]][npm-url]
[![build status][travis-image]][travis-url]
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[![Test coverage][coveralls-image]][coveralls-url]
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[![OpenCollective Backers][backers-image]](#backers)
[![OpenCollective Sponsors][sponsors-image]](#sponsors)
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Expressive, light-weight HTTP framework for node.js to make web applications and APIs more enjoyable to write. Koa requests flow through middleware 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.
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Only methods that are common to nearly all HTTP servers are integrated directly into Koa's small ~550 SLOC codebase. This
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includes things like content negotiation, normalization of node inconsistencies, redirection, and a few others.
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Koa is not bundled with any middleware, but there is a [large collection ](https://github.com/koajs/koa/wiki ) of community middleware to choose from.
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## Installation
```
$ npm install koa
```
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Koa is supported in node v4+ and node v0.12 with the `--harmony-generators` or `--harmony` flag.
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## Koa v2
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Koa v2 is currently released with the `next` tag (meaning it will not be marked as latest).
You can install it with semver:
```bash
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npm install koa@next
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```
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In this new version, the middleware function signature changes to adopt async/await:
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```js
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// Koa application is now a class and requires the new operator.
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const app = new Koa();
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// uses async arrow functions
app.use(async (ctx, next) => {
try {
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await next(); // next is now a function
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} catch (err) {
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ctx.body = { message: err.message };
ctx.status = err.status || 500;
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}
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});
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app.use(async ctx => {
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const user = await User.getById(ctx.session.userid); // await instead of yield
ctx.body = user; // ctx instead of this
});
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```
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Until async/await is natively supported in Node Koa 1.x is the official release, however you may wish to adopt 2.x early by using Babel to compile. Koa 1.x generator-based middleware may be "upgraded" to the 2.x flavour using [koa-convert ](https://github.com/koajs/convert ).
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To learn more about Koa v2, follow [this issue ](https://github.com/koajs/koa/issues/533 ) or read the docs here: https://github.com/koajs/koa/tree/v2.x/docs.
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## Community
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- [API ](docs/api/index.md ) documentation
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- [Badgeboard ](https://koajs.github.io/badgeboard ) and list of official modules
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- [Examples ](https://github.com/koajs/examples )
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- [Middleware ](https://github.com/koajs/koa/wiki ) list
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- [Wiki ](https://github.com/koajs/koa/wiki )
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- [G+ Community ](https://plus.google.com/communities/101845768320796750641 )
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- [Reddit Community ](https://www.reddit.com/r/koajs )
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- [Mailing list ](https://groups.google.com/forum/#!forum/koajs )
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- [Guide ](docs/guide.md )
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- [FAQ ](docs/faq.md )
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- [中文文档 ](https://github.com/guo-yu/koa-guide )
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- __[#koajs]__ on freenode
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## Getting started
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- [Kick-Off-Koa ](https://github.com/koajs/kick-off-koa ) - An intro to koa via a set of self-guided workshops.
- [Workshop ](https://github.com/koajs/workshop ) - A workshop to learn the basics of koa, Express' spiritual successor.
- [Introduction Screencast ](http://knowthen.com/episode-3-koajs-quickstart-guide/ ) - An introduction to installing and getting started with Koa
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## Example
```js
var koa = require('koa');
var app = koa();
// logger
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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);
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});
// response
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app.use(function *(){
this.body = 'Hello World';
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});
app.listen(3000);
```
## Running tests
```
$ make test
```
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## Authors
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- [TJ Holowaychuk ](https://github.com/tj )
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- [Jonathan Ong ](https://github.com/jonathanong )
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- [Julian Gruber ](https://github.com/juliangruber )
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- [Yiyu He ](https://github.com/dead-horse )
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## Backers
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Support us with a monthly donation and help us continue our activities.
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## Sponsors
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Become a sponsor and get your logo on our README on Github with a link to your site.
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# License
MIT
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[npm-image]: https://img.shields.io/npm/v/koa.svg?style=flat-square
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[npm-url]: https://www.npmjs.com/package/koa
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[travis-image]: https://img.shields.io/travis/koajs/koa/v1.x.svg?style=flat-square
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[travis-url]: https://travis-ci.org/koajs/koa
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[coveralls-image]: https://img.shields.io/codecov/c/github/koajs/koa.svg?style=flat-square
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[coveralls-url]: https://codecov.io/github/koajs/koa?branch=v1.x
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[backers-image]: https://opencollective.com/koajs/backers/badge.svg?style=flat-square
[sponsors-image]: https://opencollective.com/koajs/sponsors/badge.svg?style=flat-square
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[gitter-image]: https://img.shields.io/gitter/room/koajs/koa.svg?style=flat-square
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[gitter-url]: https://gitter.im/koajs/koa?utm_source=badge& utm_medium=badge& utm_campaign=pr-badge& utm_content=badge
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[#koajs]: https://webchat.freenode.net/?channels=#koajs
