Koa 洋葱模型简单实现

直接上代码

const http = require("http");

class Koa {
  constructor() {
    this.middleware = [];
  }
  use(fn) {
    this.middleware.push(fn);
  }
  listen(port) {
    let middleware = this.middleware;
    let _this=this;
    function serverFunc(req, res) {
      let context = {
        req,
        res,
        ctx:_this
      };
      let length = middleware.length;
      run(0);
      function run(n) {
        if (n < length) {
          const fn = middleware[n];
          try {
            return Promise.resolve(fn(context, run.bind(null, n + 1)));
          } catch (err) {
            return Promise.reject(err);
          }
        } else if (n === length) {
          return Promise.resolve();
        }
      }
    }
    const app = http.createServer(serverFunc);
    _this.app=app;
    app.listen(port);
  }
}

测试

const app = new Koa();
app.use(async (ctx, next) => {
  console.log("one start");
  await next();
  console.log("one end");
});
app.use(async (ctx, next) => {
  console.log("22222 start");
  await next();
  console.log("22222 end");
});
app.use(async (ctx, next) => {
  console.log("33333 start");
  await next();
  console.log("33333 end");
});
app.listen(19191);

运行，在浏览器中访问http://localhost:19191/，运行结果 如下

one start
22222 start
33333 start
33333 end
22222 end
one end