Netlify functions not working with ESM; always build to module.exports CJS syntax even with package.json "type" set to "module"

[CCBaxter84]

Describe the bug

In a simple app I just began today, Netlify functions aren't working with ESM. Despite setting node_bundler = "esbuild" in my netlify.toml file, the bundled version of my functions file still includes "CJS module.exports" syntax, which throw errors in testing:

package.json set for "module"

Of note, if I set my project to use CJS by removing "type": "module" from package.json, then the functions work:

Steps to reproduce

In a Vite Vue 3 app with Netlify globally installed

1. Use provided netlify.toml file in Configuration section
2. Create functions folder with following test.js file:

const handler = async (event, context) => {
  return {
    statusCode: 200,
    body: JSON.stringify({ message: "test" })
  }
}

export { handler }

3. Run netlify dev
4. Test netlify function: in VSCode, I'm using the REST client with following code within an apiTests.http file: get http://localhost:<port>/.netlify/functions/test

Configuration

[build] functions = "functions"

[build.environment] NODE_VERSION = "20.11.1"

[functions] directory = "functions" node_bundler = "esbuild"

Environment

System: OS: macOS 14.0 CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz Memory: 11.95 GB / 32.00 GB Shell: 5.9 - /bin/zsh Binaries: Node: 20.11.1 - ~/.nvm/versions/node/v20.11.1/bin/node npm: 10.2.4 - ~/.nvm/versions/node/v20.11.1/bin/npm npmGlobalPackages: netlify-cli: 17.19.3