简易 Koa 洋葱模型

手写 Koa 洋葱模型

效果如下

const app = new Koa()
app.use(async (next) => {
  console.log(1)
  await next()
  console.log(2)
})
app.use(async (next) => {
  console.log(3)
  await next()
  console.log(4)
})
app.compose()
// 打印1,3,2,4

function compose(...funcs) {
  return function (v) {
    return funcs.reduce((p, cb) => {
      return p.then(() => cb)
    }, v)
  }
}

class Koa {
  constructor() {
    this.middleware = []
  }
  compose() {
    const resolve = () => {}
    const reject = () => {}
    const dispatch = (i) => {
      const fn = this.middleware[i]
      if (!fn) return Promise.resolve()
      return Promise.resolve(
        fn(() => {
          return dispatch(i + 1)
        })
      )
    }
    return dispatch(0)
  }
  use(cb) {
    this.middleware.push(cb)
  }
}