290 lines
17 KiB
Markdown
290 lines
17 KiB
Markdown
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<img src="/docs/logo.png" alt="Koa middleware framework for nodejs"/>
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[![gitter][gitter-image]][gitter-url]
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[![NPM version][npm-image]][npm-url]
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[![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)
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[![OpenCollective Sponsors][sponsors-image]](#sponsors)
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[![PR's Welcome][pr-welcoming-image]][pr-welcoming-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
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Koa requires __node v7.6.0__ or higher for ES2015 and async function support.
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```
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$ npm install koa
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```
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## Hello Koa
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```js
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const Koa = require('koa');
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const app = new Koa();
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// response
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app.use(ctx => {
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ctx.body = 'Hello Koa';
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});
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app.listen(3000);
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```
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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.
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- [Workshop](https://github.com/koajs/workshop) - A workshop to learn the basics of Koa, Express' spiritual successor.
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- [Introduction Screencast](https://knowthen.com/episode-3-koajs-quickstart-guide/) - An introduction to installing and getting started with Koa
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## Middleware
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Koa is a middleware framework that can take two different kinds of functions as middleware:
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* async function
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* common function
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Here is an example of logger middleware with each of the different functions:
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### ___async___ functions (node v7.6+)
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```js
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app.use(async (ctx, next) => {
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const start = Date.now();
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await next();
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const ms = Date.now() - start;
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console.log(`${ctx.method} ${ctx.url} - ${ms}ms`);
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});
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```
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### Common function
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```js
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// Middleware normally takes two parameters (ctx, next), ctx is the context for one request,
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// next is a function that is invoked to execute the downstream middleware. It returns a Promise with a then function for running code after completion.
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app.use((ctx, next) => {
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const start = Date.now();
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return next().then(() => {
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const ms = Date.now() - start;
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console.log(`${ctx.method} ${ctx.url} - ${ms}ms`);
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});
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});
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```
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### Koa v1.x Middleware Signature
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The middleware signature changed between v1.x and v2.x. The older signature is deprecated.
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**Old signature middleware support will be removed in v3**
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Please see the [Migration Guide](docs/migration.md) for more information on upgrading from v1.x and
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using v1.x middleware with v2.x.
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## Context, Request and Response
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Each middleware receives a Koa `Context` object that encapsulates an incoming
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http message and the corresponding response to that message. `ctx` is often used
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as the parameter name for the context object.
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```js
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app.use(async (ctx, next) => { await next(); });
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```
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Koa provides a `Request` object as the `request` property of the `Context`.
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Koa's `Request` object provides helpful methods for working with
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http requests which delegate to an [IncomingMessage](https://nodejs.org/api/http.html#http_class_http_incomingmessage)
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from the node `http` module.
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Here is an example of checking that a requesting client supports xml.
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```js
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app.use(async (ctx, next) => {
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ctx.assert(ctx.request.accepts('xml'), 406);
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// equivalent to:
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// if (!ctx.request.accepts('xml')) ctx.throw(406);
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await next();
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});
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```
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Koa provides a `Response` object as the `response` property of the `Context`.
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Koa's `Response` object provides helpful methods for working with
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http responses which delegate to a [ServerResponse](https://nodejs.org/api/http.html#http_class_http_serverresponse)
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.
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Koa's pattern of delegating to Node's request and response objects rather than extending them
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provides a cleaner interface and reduces conflicts between different middleware and with Node
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itself as well as providing better support for stream handling. The `IncomingMessage` can still be
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directly accessed as the `req` property on the `Context` and `ServerResponse` can be directly
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accessed as the `res` property on the `Context`.
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Here is an example using Koa's `Response` object to stream a file as the response body.
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```js
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app.use(async (ctx, next) => {
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await next();
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ctx.response.type = 'xml';
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ctx.response.body = fs.createReadStream('really_large.xml');
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});
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```
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The `Context` object also provides shortcuts for methods on its `request` and `response`. In the prior
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examples, `ctx.type` can be used instead of `ctx.response.type` and `ctx.accepts` can be used
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instead of `ctx.request.accepts`.
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For more information on `Request`, `Response` and `Context`, see the [Request API Reference](docs/api/request.md),
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[Response API Reference](docs/api/response.md) and [Context API Reference](docs/api/context.md).
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## Koa Application
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The object created when executing `new Koa()` is known as the Koa application object.
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The application object is Koa's interface with node's http server and handles the registration
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of middleware, dispatching to the middleware from http, default error handling, as well as
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configuration of the context, request and response objects.
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Learn more about the application object in the [Application API Reference](docs/api/index.md).
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## Documentation
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- [Usage Guide](docs/guide.md)
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- [Error Handling](docs/error-handling.md)
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- [Koa for Express Users](docs/koa-vs-express.md)
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- [FAQ](docs/faq.md)
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- [API documentation](docs/api/index.md)
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## Troubleshooting
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Check the [Troubleshooting Guide](docs/troubleshooting.md) or [Debugging Koa](docs/guide.md#debugging-koa) in
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the general Koa guide.
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## Running tests
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```
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$ npm test
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```
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## Reporting vulnerabilities
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To report a security vulnerability, please do not open an issue, as this notifies attackers of the vulnerability. Instead, please email [dead_horse](mailto:heyiyu.deadhorse@gmail.com), [jonathanong](mailto:me@jongleberry.com), and [niftylettuce](mailto:niftylettuce@gmail.com) to disclose.
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## Authors
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See [AUTHORS](AUTHORS).
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## Community
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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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- [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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- [中文文档 v1.x](https://github.com/guo-yu/koa-guide)
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- [中文文档 v2.x](https://github.com/demopark/koa-docs-Zh-CN)
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- __[#koajs]__ on freenode
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## Job Board
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Looking for a career upgrade?
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<a href="https://astro.netlify.com/automattic"><img src="https://astro.netlify.com/static/automattic.png"></a>
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<a href="https://astro.netlify.com/segment"><img src="https://astro.netlify.com/static/segment.png"></a>
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<a href="https://astro.netlify.com/auth0"><img src="https://astro.netlify.com/static/auth0.png"/></a>
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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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<a href="https://opencollective.com/koajs/backer/0/website" target="_blank"><img src="https://opencollective.com/koajs/backer/0/avatar.svg"></a>
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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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<a href="https://opencollective.com/koajs/sponsor/0/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/0/avatar.svg"></a>
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<a href="https://opencollective.com/koajs/sponsor/19/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/19/avatar.svg"></a>
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<a href="https://opencollective.com/koajs/sponsor/20/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/20/avatar.svg"></a>
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<a href="https://opencollective.com/koajs/sponsor/21/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/21/avatar.svg"></a>
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<a href="https://opencollective.com/koajs/sponsor/22/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/22/avatar.svg"></a>
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||
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<a href="https://opencollective.com/koajs/sponsor/23/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/23/avatar.svg"></a>
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<a href="https://opencollective.com/koajs/sponsor/24/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/24/avatar.svg"></a>
|
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<a href="https://opencollective.com/koajs/sponsor/25/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/25/avatar.svg"></a>
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<a href="https://opencollective.com/koajs/sponsor/26/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/26/avatar.svg"></a>
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<a href="https://opencollective.com/koajs/sponsor/27/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/27/avatar.svg"></a>
|
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<a href="https://opencollective.com/koajs/sponsor/28/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/28/avatar.svg"></a>
|
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<a href="https://opencollective.com/koajs/sponsor/29/website" target="_blank"><img src="https://opencollective.com/koajs/sponsor/29/avatar.svg"></a>
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# License
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[MIT](https://github.com/koajs/koa/blob/master/LICENSE)
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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/master.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=master
|
||
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[backers-image]: https://opencollective.com/koajs/backers/badge.svg?style=flat-square
|
||
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[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
|
||
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[pr-welcoming-image]: https://img.shields.io/badge/PRs-welcome-brightgreen.svg?style=flat-square
|
||
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[pr-welcoming-url]: https://github.com/koajs/koa/pull/new
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