koa中间件

koa.middleware.js

const middleware = []
let mw1 = async function (ctx, next) {
  console.log("next前，第一个中间件", new Date().getTime())
  await next()
  console.log("next后，第一个中间件", new Date().getTime())
}
let mw2 = async function (ctx, next) {
  console.log("next前，第二个中间件", new Date().getTime())
  await next()
  console.log("next后，第二个中间件", new Date().getTime())
}
let mw3 = async function (ctx, next) {
  console.log("第三个中间件，没有next了", new Date().getTime())
}


function use(mw) {
  middleware.push(mw)
}

use(mw1)
use(mw2)
use(mw3)

let fn = function (ctx) {
  return dispatch(0)

  function dispatch(i) {
    let currentMW = middleware[i]
    if (!currentMW) {
      return Promise.reject('没有中间件')
    }
    return currentMW(ctx, dispatch.bind(null, i+1))
  }
}

fn()