原文

koa middleware framework for nodejs

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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.

Node.js中丰富的HTTP中间件框架让Web应用和API的开发和编码充满乐趣。Koa的中间件逐层响应输入的数据，之后再逐层过滤和处理输出的数据，中间件组织成层层包裹的结构。

Only methods that are common to nearly all HTTP servers are integrated directly into Koa’s small ~570 SLOC codebase. This includes things like content negotiation, normalization of node inconsistencies, redirection, and a few others.

Koa的核心代码库不超过570行，仅实现了常见HTTP服务器的基础方法。主要包含内容协商，节点差异处理和重定向等等。

Koa is not bundled with any middleware.

Koa没有内置任何中间件。

安装（Installation）

Koa requires node v4.0.0 or higher for (partial) ES2015 support.

Koa要求node v4.0.0或以上版本，以满足对ES2015规范的部分要求。

$ npm install koa@next

Hello koa

const Koa = require('koa');
const app = new Koa();

// response
app.use(ctx => {
  ctx.body = 'Hello Koa';
});

app.listen(3000);

入门（Getting started）

中间件（Middleware）

Koa is a middleware framework that can take 3 different kinds of functions as middleware:

  • common function
  • async function
  • generatorFunction

Koa是一个中间件框架，可以使用如下3中方式的函数作为中间件：

  • 普通函数
  • 异步函数
  • 生成器函数

Here is an example of logger middleware with each of the different functions:

下面这个例子是一个日志记录中间件的不同实现方式：

（普通函数）Common function

// Middleware normally takes two parameters (ctx, next), ctx is the context for one request,
// 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.

app.use((ctx, next) => {
  const start = new Date();
  return next().then(() => {
    const ms = new Date() - start;
    console.log(`${ctx.method} ${ctx.url} - ${ms}ms`);
  });
});

异步函数（async functions (Babel required)）

（编者按：在Node.js 7.0中启用–harmony-async-await标记即可可代替Babel）。

app.use(async (ctx, next) => {
  const start = new Date();
  await next();
  const ms = new Date() - start;
  console.log(`${ctx.method} ${ctx.url} - ${ms}ms`);
});

生成器函数（GeneratorFunction）

To use generator functions, you must use a wrapper such as co that is no longer supplied with Koa.

需要注意的是：使用生成器函数，必须用co之类的库对其进行封装，Koa不在提供此类对象。

app.use(co.wrap(function *(ctx, next) {
  const start = new Date();
  yield next();
  const ms = new Date() - start;
  console.log(`${ctx.method} ${ctx.url} - ${ms}ms`);
}));

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. It is however recommended that you choose to migrate all v1.x middleware as soon as possible.

// 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.

const convert = require('koa-convert');

app.use(convert(function *(next) {
  const start = new Date();
  yield next;
  const ms = new Date() - start;
  console.log(`${this.method} ${this.url} - ${ms}ms`);
}));

Babel设置（Babel setup）

For Node 4.0 and Babel 6.0 you can setup like this:

基于Node 4.0和Babel 6.0可以进行如下设置：

$ npm install babel-register babel-plugin-transform-async-to-generator --save

// set babel in entry file
require('babel-register')({
  plugins: ['transform-async-to-generator']
});

Check out an example in koa’s test.

可以签出这个Koa的测试代码测试一下。

运行测试（Running tests）

$ make test

作者（Authors）

See AUTHORS.

社区贡献（Community）

许可（License）

MIT