koa-lite/Readme.md

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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]
[![Test coverage][coveralls-image]][coveralls-url]
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Expressive HTTP middleware framework for node.js to make web applications and APIs more enjoyable to write. Koa's middleware stack flows in a stack-like manner, allowing you to perform actions downstream then filter and manipulate the response upstream.
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Only methods that are common to nearly all HTTP servers are integrated directly into Koa's small ~570 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.
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## Installation
Koa requires __node v4.0.0__ or higher for (partial) ES2015 support.
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```
$ npm install koa@next
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```
## Hello koa
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```js
const Koa = require('koa');
const app = new Koa();
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// response
app.use(ctx => {
ctx.body = 'Hello Koa';
});
app.listen(3000);
```
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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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## Middleware
Koa is an middleware framework, it can take 3 different kind function as middleware:
* common function
* async function
* generatorFunction
Here we write an logger middleware with different function.
### Common function
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```js
// Middleware normally take two parameters (ctx, next), ctx is the context for one request,
// next is an function that is invoked to execute the downstream middleware. It returns a Promise with a then function for running code after completion.
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app.use((ctx, next) => {
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const start = new Date();
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return next().then(() => {
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const ms = new Date() - start;
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console.log(`${ctx.method} ${ctx.url} - ${ms}ms`);
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});
});
```
### ___async___ functions (Babel required)
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```js
app.use(async (ctx, next) => {
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const start = new Date();
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await next();
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const ms = new Date() - start;
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console.log(`${ctx.method} ${ctx.url} - ${ms}ms`);
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});
```
### GeneratorFunction
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To use generator functions, you must use a wrapper such as [co](https://github.com/tj/co) that is no longer supplied with Koa.
```js
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app.use(co.wrap(function *(ctx, next) {
const start = new Date();
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yield next();
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const ms = new Date() - start;
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console.log(`${ctx.method} ${ctx.url} - ${ms}ms`);
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}));
```
### Old signature middleware (v1.x) - Deprecated
**Old signature middleware (v1.x) support will be removed in v3**
Koa v2.x will try to convert legacy signature, generator middleware on `app.use`, using [koa-convert](https://github.com/koajs/convert).
It is however recommended that you choose to migrate all v1.x middleware as soon as possible.
```js
// Koa will convert
app.use(function *(next) {
const start = new Date();
yield next;
const ms = new Date() - start;
console.log(`${this.method} ${this.url} - ${ms}ms`);
});
```
You could do it manually as well, in which case Koa will not convert.
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```js
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const convert = require('koa-convert');
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app.use(convert(function *(next) {
const start = new Date();
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yield next;
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const ms = new Date() - start;
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console.log(`${this.method} ${this.url} - ${ms}ms`);
}));
```
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## Babel setup
For Node 4.0 and Babel 6.0 you can setup like this
```bash
// install babel and required presets
$ npm install babel-core --save
$ npm install babel-preset-es2015-node5 --save
$ npm install babel-preset-stage-3 --save
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```
```js
// set babel in entry file
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require('babel-core/register')({
presets: ['es2015-node5', 'stage-3']
});
```
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## Running tests
```
$ make test
```
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## Authors
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See [AUTHORS](AUTHORS).
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## Community
- [API](docs/api/index.md) documentation
- [Badgeboard](https://koajs.github.io/badgeboard) and list of official modules
- [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)
- [Reddit Community](https://www.reddit.com/r/koajs)
- [Mailing list](https://groups.google.com/forum/#!forum/koajs)
- [Guide](docs/guide.md)
- [FAQ](docs/faq.md)
- [中文文档](https://github.com/guo-yu/koa-guide)
- __[#koajs]__ on freenode
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# License
MIT
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[npm-image]: https://img.shields.io/npm/v/koa.svg?style=flat-square
[npm-url]: https://www.npmjs.com/package/koa
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[travis-image]: https://img.shields.io/travis/koajs/koa/master.svg?style=flat-square
[travis-url]: https://travis-ci.org/koajs/koa
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[coveralls-image]: https://codecov.io/github/koajs/koa/coverage.svg?branch=master
[coveralls-url]: https://codecov.io/github/koajs/koa?branch=master
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[gitter-image]: https://badges.gitter.im/Join%20Chat.svg
[gitter-url]: https://gitter.im/koajs/koa?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge
[#koajs]: https://webchat.freenode.net/?channels=#koajs