koa中间件机制

async function job1(ctx, next) {
  console.log(ctx.name, "1")
  await next()
  console.log(ctx.name, "5")
}

async function job2(ctx, next) {
  console.log(ctx.name, "2")
  await next()
  console.log(ctx.name, "4")
}

async function job3(ctx) {
  console.log(ctx.name, "3")
}

const ctx = { name: "koa" }

原理就是把下一个 promise 传给上一个

const process = (...jobs) =>
  jobs.reduceRight((next, job) => async () => await job(ctx, next), null)

process(job1, job2, job3)() // koa 1, koa 2, koa 3, koa 4, koa 5