怎样开发一个最简版 Koa 日志打印中间件

index.js

const Koa = require("koa");
const app = new Koa();

/**
 * a simple log middleware
 * @param {object} ctx
 */
function logger() {
  return async function (ctx, next) {
    console.log(ctx.method, ctx.header.host, ctx.url);
    await next();
  };
}

app.use(logger());
app.use((ctx) => {
  ctx.body = "Hello, World!";
});

app.listen(3000);