Get esbuild to watch for changes, rebuild, and restart express server

I am trying to create a simple SSR powered project using express + react. To do this, I need to simultaneously watch frontend and backend scripts during development.

The goal here is to use express routes to point to react page components. Now, I have this working, but I am having problems with DX.

Here are my package scripts:

    "build:client": "esbuild src/index.js --bundle --outfile=public/bundle.js --loader:.js=jsx",
    "build:server": "esbuild src/server.jsx --bundle --outfile=public/server.js --platform=node",
    "build": "npm run build:client && npm run build:server",
    "start": "node ./public/server.js"

Now this works if I do npm run build && npm run start, but the problem is that it doesn't watch for changes and rebuild the frontend bundle or restart the backend server.

Now, if I add --watch to the 2 build scripts, it only starts watching the index.js file and does not execute the other scripts.

So if I add nodemon to my start script, it doesn't matter because esbuild won't get past the first script due to the watcher.

Is there a simpler way of doing what I am trying to do here? I also want to add tailwind to this project once I figure this out, so any tips around that would be helpful as well.

I would suggest using the JS interface to esbuild, i.e., write a small JS script that requires esbuild and runs it, and then use the functional version of https://esbuild.github.io/api/#watch. Something like this:

require('esbuild').build({
  entryPoints: ['app.js'],
  outfile: 'out.js',
  bundle: true,
  watch: {
    onRebuild(error, result) {
      if (error) console.error('watch build failed:', error)
      else { 
        console.log('watch build succeeded:', result)
        // HERE: somehow restart the server from here, e.g., by sending a signal that you trap and react to inside the server.
      }
    },
  },
}).then(result => {
  console.log('watching...')
})

Update

To get the same behavior in esbuild 0.17+:

const config = {
  // entryPoints:
  // ...
  plugins: [{
    name: 'rebuild-notify',
    setup(build) {
      build.onEnd(result => {
        console.log(`build ended with ${result.errors.length} errors`);
        // HERE: somehow restart the server from here, e.g., by sending a signal that you trap and react to inside the server.
      })
    },
  }],
};

const run = async () => {
  const ctx = await esbuild.context(config);
  await ctx.watch();
};

run();