写一个例子理解koa-compose的用法及函数结果顺序

我们知道koa-compose 是koa框架实现洋葱包裹型中间件的基础，通过一段简短的代码来理解它的使用方式及结果顺序

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

const composes = [];

function use(fun) {
  composes.push(fun);
}

use(async (ctx, next) => {
  console.log('第一个中间件');
  await next();
  console.log('1->END');
});

use(async (ctx, next) => {
  console.log('第二个中间件');
  await next();
  console.log('2->END');
});

use(async (ctx, next) => {
  console.log('第三个中间件');
  await next();
  console.log('3->END');
});

const exec = compose(composes);

(async () => {
  const ctx = {};
  await exec(ctx, async () => {
    console.log('END');
  });
})();

结果如下