koa/koa-vs-express.md at master koajs/koa

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koa/koa-vs-express.md at master · koajs/koa
Philosophically, Koa aims to "fix and replace node", whereas Express "augments node".Koa uses promises and async functions to rid apps of callback hell and…

August 30, 2019 at 04:32PM
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function compose(middlewares) {
  return function middleware(ctx, next) {
    let index = -1;
    function dispatch(n) {
      if (n <= index) return Promise.reject(new Error('multitime call midware'));
      index = n;
      let fn = middlewares[n];
      if (n === middlewares.length) fn = next;
      if (!fn) return Promise.resolve();

      try {
        return Promise.resolve(fn(ctx, () => dispatch(n + 1)));
      } catch (error) {
        return Promise.reject(error);
      }
    }

    return dispatch(0);
  };
}

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简单模拟

function express() {
  const app = { middlewares: [] };
  app.use = function use(middleware) {
    app.middlewares.push(middleware);
  };

  const req = {};
  const res = {};
  let i = 0;
  function next() {
    if (i === app.middlewares.length) {
      return;
    }
    const fn = app.middlewares[i++];
    fn.call(app, req, res, next);
  }

  app.listen = function listen(port, callback) {
    callback(port);
    next();
  };

  return app;
}

const app = express();
app.use((req, res, next) => {
  console.log('ss1');
  req.body = { name: 'as' };
  next();
  console.log('ss2');
});

app.use((req, res, next) => {
  console.log(req);
  console.log('ss4');
  next();
  console.log('ss5');
});

app.listen(3000, (port) => {
  console.log('listen start', port);
});