Express服务器端代码热加载的实现代码

mkdir your-project
cd your-project
npm init -y
npm install --save express

// ./src/main.js
const express = require('express');

function bootstrap() {
  const app = express();

  app.all('*', (req, res) => {
    res.send(`hello, world!\n`);
  });

  app.listen(3000, function () {
    console.log('listen on http://localhost:3000');
  });
}

bootstrap();

{
  ...
  "scripts": {
    "start": "node src/main.js"
  },
  ...
}

npm run start

npm install --save-dev nodemon

{
  ...
  "scripts": {
    "dev": "nodemon src/main.js",
    "start": "node src/main.js"
  }
  ...
}

{
  "watch": ["src/"],
  "ext": "js",
  "ignore": ["*.test.js", "*.spec.js"]
}

npm install --save-dev webpack webpack-cli webpack-node-externals run-script-webpack-plugin rimraf

// ./src/count.js
let n = 0;

export function inc() {
  n++;
  return n;
}

// ./src/hello.js
export function greet(name = 'World') {
  return `Hello, ${name}!`;
}

// ./src/main.js
import express from 'express';
import { createServer } from 'http';
import { inc } from './count';
import { greet } from './hello';

function bootstrap() {
  const app = express();

  // 默认情况下 express 会自动创建 server，这里手动创建 server 
  // 是为了在后面调用 server.close() 关闭旧的服务
  const server = createServer(app);

  app.all('*', (req, res) => {
    const n = inc();
    res.send(`${n}: ${greet('bob')}\n`);
  });

  server.listen(3000, function () {
    console.log('listen on http://localhost:3000');
  });

  if (module.hot) {
    module.hot.accept();
    module.hot.dispose(() => server.close());
  }
}

bootstrap();

{
  ...
  "scripts": {
    "dev": "rimraf dist && webpack --config webpack-hmr.config.js --watch",
    "build": "rimraf dist && webpack --config webpack.config.js",
    "start": "node dist/server.js"
  },
  ...
}

// ./webpack.config.js
const path = require('path');
const nodeExternals = require('webpack-node-externals');

module.exports = {
  mode: 'production',
  entry: ['./src/main.js'],
  target: 'node',
  externals: [nodeExternals()],
  resolve: {
    extensions: ['.js'],
  },
  output: {
    path: path.join(__dirname, 'dist'),
    filename: 'server.js',
  },
};

// ./webpack-hmr.config.js
const webpack = require('webpack');
const path = require('path');
const nodeExternals = require('webpack-node-externals');
const { RunScriptWebpackPlugin } = require('run-script-webpack-plugin');

module.exports = {
  mode: 'development',
  entry: ['webpack/hot/poll?100', './src/main.js'],
  target: 'node',
  externals: [
    nodeExternals({
      allowlist: ['webpack/hot/poll?100'],
    }),
  ],
  resolve: {
    extensions: ['.js'],
  },
  plugins: [
    new webpack.HotModuleReplacementPlugin(),
    new RunScriptWebpackPlugin({ name: 'server.js', autoRestart: false }),
  ],
  output: {
    path: path.join(__dirname, 'dist'),
    filename: 'server.js',
  },
};

curl http://localhost:3000/

...
asset server.js 46.1 KiB [emitted] (name: main)
asset main.44ac5c7bc9372be2efa5.hot-update.js 2.58 KiB [emitted] [immutable] [hmr] (name: main)
asset main.44ac5c7bc9372be2efa5.hot-update.json 28 bytes [emitted] [immutable] [hmr]
Entrypoint main 48.7 KiB = server.js 46.1 KiB main.44ac5c7bc9372be2efa5.hot-update.js 2.58 KiB
runtime modules 23.5 KiB 9 modules
cached modules 4.69 KiB [cached] 7 modules
./src/main.js 677 bytes [built] [code generated]
webpack 5.89.0 compiled successfully in 32 ms
[HMR] Updated modules:
[HMR]  - ./src/main.js
[HMR] Update applied.
listen on http://localhost:3000/

curl http://localhost:3000/

...
asset server.js 46.1 KiB [emitted] (name: main)
asset main.56dcdc90891aac75fe1c.hot-update.js 1.37 KiB [emitted] [immutable] [hmr] (name: main)
asset main.56dcdc90891aac75fe1c.hot-update.json 28 bytes [emitted] [immutable] [hmr]
Entrypoint main 47.5 KiB = server.js 46.1 KiB main.56dcdc90891aac75fe1c.hot-update.js 1.37 KiB
runtime modules 23.5 KiB 9 modules
cached modules 5.28 KiB [cached] 7 modules
./src/hello.js 72 bytes [built] [code generated]
webpack 5.89.0 compiled successfully in 65 ms
[HMR] Updated modules:
[HMR]  - ./src/hello.js
[HMR]  - ./src/main.js
[HMR] Update applied.
listen on http://localhost:3000/

curl http://localhost:3000/

// ./src/main.js
// ...
import { readdir } from 'fs/promises';
import { resolve } from 'path';

async function bootstrap() {
  // ...
  const server = createServer(app);

  // 动态加载 controllers 目录下的所有文件
  await loadControllers(app);

  app.all('*', (req, res) => { /* ... */ });
  //...
}

async function loadControllers(app) {
  try {
    // 注意，这里应该是扫描 src 目录，而不是 dist 目录
    const files = await readdir(resolve('./src/controllers'));
    for (let i = 0; i < files.length; i++) {
      const file = files[i];
      const name = file.substring(0, file.length - 3); // remove ext '.js'
      const module = await import('./controllers/' + name);
      app.use(`/${name}`, module.default);
    }
  } catch (err) {
    console.error(err);
  }
}

bootstrap();

// 编译后的代码会提示找不到目录 ./dist/controllers 
readdir(path.join(__dirname, 'controllers')); 

readdir(path.resolve('./src/controllers'));

// ./src/controllers/posts.js
import { Router } from 'express';

const router = Router();

router.get('/', (req, res) => {
  res.send([
    {
      id: 1,
      title: 'post 1',
      content: 'content of the post',
    },
  ]);
});

export default router;

curl http://localhost:3000/posts

[{"id":1,"title":"post 1","content":"content of the post"}]

// 显示声明有哪些 controllers
const controllerNames = [
  'posts',
];

async function loadControllers(app) {
  const controllers = controllerNames.map((name) => ({ name }));
  for (let i = 0; i < controllers.length; i++) {
    const controller = controllers[i];
    try {
      const module = await import(`./controllers/${controller.name}`);
      controller.router = module.default;
    } catch (err) {
      // console.error(err);
    }
  }

  controllers.forEach(({ name, router }) => {
    if (router) {
      const path = `/${name}`;
      app.use(path, router);
      console.log(`mount controller '${name}' on '${path}'`);
    } else {
      console.error(`cannot find controller '${name}'`);
    }
  });
}