Extend BFF Server#

In some applications, developers may want to handle all BFF functions uniformly, such as for authentication, logging, data processing, etc.

Modern.js provides two methods that allow developers to extend the BFF Server freely according to the runtime framework.

Middleware#

Developers can write middleware in the api/_app.ts file to extend the BFF Server. Taking Express as the runtime framework, here is an example of how to write a middleware to add permission checks:

import { hook } from '@modern-js/runtime/server';
import { Request, Response, NextFunction } from 'express';

export default hook(({ addMiddleware }) => {
  addMiddleware(async (req: Request, res: Response, next: NextFunction) => {
    if (req.url !== '/api/login') {
      const sid = req?.cookies?.sid;
      if (!sid) {
        res.status(400);
        res.json({ code: -1, message: 'need login' });
      } else {
        next();
      }
    } else {
      next();
    }
  });
});

Then add a standard BFF function api/lambda/hello.ts:

export default async () => {
  return 'Hello Modern.js';
};

Next, in the frontend, add the code to access the API in src/routes/page.tsx, directly using the integrated method for the call:

import { useState, useEffect } from 'react';
import { get as hello } from '@api/hello';

export default () => {
  const [text, setText] = useState('');

  useEffect(() => {
    async function fetchMyApi() {
      const { message } = await hello();
      setText(message);
    }

    fetchMyApi();
  }, []);

  return <p>{text}</p>;
};

Now run the dev command to start the project, and visit http://localhost:8080/. You will find that the request to /api/hello is intercepted:

Finally, modify the frontend code in src/routes/page.tsx to call the login interface before accessing /api/hello:

import { useState, useEffect } from 'react';
import { get as hello } from '@api/hello';
import { post as login } from '@api/login';

export default () => {
  const [text, setText] = useState('');

  useEffect(() => {
    async function fetchAfterLogin() {
      const { code } = await login();
      if (code === 0) {
        const { message } = await hello();
        setText(message);
      }
    }
    fetchAfterLogin();
  }, []);

  return <p>{text}</p>;
};

Refresh the page to see that the access to /api/hello is successful:

The above code simulates adding middleware in api/_app.ts to implement simple login functionality. Similarly, other functionalities can be implemented in this hook file to extend the BFF Server.

Define Server Instance#

In addition to middleware, you can also define a BFF Server instance via the api/app.ts. Developers need to export an instance that can be recognized by the runtime framework plugin. Here is a simple demonstration of how to define a server instance with Koa and Express.

import express from 'express';

const app = express();
app.use(async (req, res, next) => {
  console.info(`access url: ${req.url}`);
  next();
});

export default app;

In complex BFF logic, defining a server instance allows for easier organization of code logic and directory structure design through a single entry point. In this file, you can perform initialization logic, add global middleware, declare routes, and even extend the original framework.

The routes defined by the BFF functions will be registered after the routes defined in the app.ts file. Therefore, you can also intercept the routes defined by the BFF functions here for preprocessing or early responses.