Koa挂载到特定路径 koa-mount 帮助文档

简介

将其它应用程序作为中间件挂载，传递给 mount() 函数的路径参数暂时从 URL 里剥离出来，直到堆栈释放。对于创建不管用于那个路径且功能正常的整个 app 或 中间件是很有用。

安装

$ npm install koa-mount

挂载应用程序

把整个应用程序挂载到一个特定的路径上，例如，你可以在/blog目录挂载一个博客程序，博客程序使用一个匹配如/、/posts的路由，挂载后，这些路由将恬当地表现为/blog/、/blog/posts。

const mount = require('koa-mount');
const Koa = require('koa');

// hello

const a = new Koa();

a.use(async function (ctx, next){
  await next();
  ctx.body = 'Hello';
});

// world

const b = new Koa();

b.use(async function (ctx, next){
  await next();
  ctx.body = 'World';
});

// app

const app = new Koa();

app.use(mount('/hello', a));
app.use(mount('/world', b));

app.listen(3000);
console.log('listening on port 3000');

尝试下面的请求：

$ GET /
Not Found

$ GET /hello
Hello

$ GET /world
World

挂载中间件

把中间件挂载到一个特定的路径上，中间件独立于这个路径动作。

const mount = require('koa-mount');
const Koa = require('koa');

async function hello(ctx, next){
  await next();
  ctx.body = 'Hello';
}

async function world(ctx, next){
  await next();
  ctx.body = 'World';
}

const app = new Koa();

app.use(mount('/hello', hello));
app.use(mount('/world', world));

app.listen(3000);
console.log('listening on port 3000');

可选的路径

挂载函数mount()的路径参数是可选的，默认值是/

app.use(mount(a));
app.use(mount(b));

调试

把DEBUG环境变量添加到koa-mount白名单调试输出：

$ DEBUG=koa-mount node myapp.js &
$ GET /foo/bar/baz

  koa-mount enter /foo/bar/baz -> /bar/baz +2s
  koa-mount enter /bar/baz -> /baz +0ms
  koa-mount enter /baz -> / +0ms
  koa-mount leave /baz -> / +1ms
  koa-mount leave /bar/baz -> /baz +0ms
  koa-mount leave /foo/bar/baz -> /bar/baz +0ms

示例

下面这个例子阐述了挂载几个应用程序，你如何实现串联效果。

/**
 * This example illustrates how you may
 * implement a cascading effect using
 * several mounted applications that
 * are not aware of where they are mounted:
 *
 * GET /foo
 * GET /foo/bar
 * GET /foo/bar/baz
 */

const mount = require('koa-mount')
const Koa = require('koa')

const app = new Koa()
const a = new Koa()
const b = new Koa()
const c = new Koa()

a.use(async function (ctx, next) {
    await next()
    if (!ctx.body) ctx.body = 'foo'
})

b.use(async function (ctx, next) {
    await next()
    if (!ctx.body) ctx.body = 'bar'
})

c.use(async function (ctx, next) {
    await next()
    ctx.body = 'baz'
})

app.use(mount('/foo', a))
a.use(mount('/bar', b))
b.use(mount('/baz', c))

app.listen(3000)
console.log('listening on port 3000')

下面示例说明以便集中地记录日志等等，应用程序错误如何向上游传播。

/**
 * This example illustrates how application
 * errors propagate upstream for
 * centralized logging etc.
 */

const mount = require('koa-mount')
const Koa = require('koa')

const a = new Koa()
const b = new Koa()
const c = new Koa()

a.use(async function (ctx, next) {
  await next()
})

b.use(async function (ctx, next) {
  await next()
})

c.use(async function (ctx, next) {
  await next()
  throw new Error('tobi escaped!')
})

a.use(mount(b))
b.use(mount(c))

// suppress stderr output if you want
a.outputErrors = false

// errors will propagate to the upstream app,
// however you can still use the "error" listener
// in subapps more specific behaviour, just keep
// in mind that it should be used in an unobtrusive way,
// since most decisions should be made by the parent app.

a.on('error', function (err, ctx) {
  console.log('%s %s: sending error "%s" to alert service',
    ctx.method,
    ctx.path,
    err.message)
})

a.listen(3000)
console.log('listening on port 3000')

错误将向上游程序传播。但是，你仍然可以在子程序中使用error侦听更具体的行为。请记住，在子程序中它应该以一种不引人注目的方式使用，因为大多数决策都应该由父应用程序作出。

下面这个例子阐述了如何像挂载应用程序一样挂载中间件。

/**
 * This example illustrates how middleware
 * may be mounted just like applications.j
 */

const mount = require('koa-mount')
const Koa = require('koa')

async function hello (ctx, next) {
  await next()
  ctx.body = 'Hello'
}

async function world (ctx, next) {
  await next()
  ctx.body = 'World'
}

const app = new Koa()

app.use(mount('/hello', hello))
app.use(mount('/world', world))

app.listen(3000)
console.log('listening on port 3000')

下面这个例子阐述了如果你只想结合行为，在没有路径时如何挂载应用程序。

/**
 * This example illustrates how applications
 * may be mounted without a pathname prefix
 * if you simply wish to combine behaviours.
 */

const mount = require('koa-mount')
const Koa = require('koa')

// GET /hello

const a = new Koa()

a.use(async function (ctx, next) {
  await next()
  if (ctx.path === '/hello') ctx.body = 'Hello'
})

// GET /world

const b = new Koa()

b.use(async function (ctx, next) {
  await next()
  if (ctx.path === '/world') ctx.body = 'World'
})

// app

const app = new Koa()

app.use(mount(a))
app.use(mount(b))

app.listen(3000)
console.log('listening on port 3000')

下面示例阐述的是将应用程序挂载到给定路径的典型模式。

/**
 * This example illustrates the typical
 * pattern of mounting an application
 * to a given pathname prefix.
 *
 * GET /hello
 * GET /world
 */

const mount = require('koa-mount')
const Koa = require('koa')

// hello

const a = new Koa()

a.use(async function (ctx, next) {
  await next()
  ctx.body = 'Hello'
})

// world

const b = new Koa()

b.use(async function (ctx, next) {
  await next()
  ctx.body = 'World'
})

// app

const app = new Koa()

app.use(mount('/hello', a))
app.use(mount('/world', b))

app.listen(3000)
console.log('listening on port 3000')