Support ESM

Right now this module doesn’t support ESM. If you try to use modules, your function will not load.

Provided module can't be loaded.
Is there a syntax error in your code?
Detailed stack trace: Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: /Users/timmerman/Documents/trash/esmtestff/index.js
require() of ES modules is not supported.

I believe there are a few things we need to do to allow functions using modules to be supported:

Repro

Allow modules in package.json

 "type": "module",

Use ESM import/export

/**
 * Send "Hello, World!"
 * @param req https://expressjs.com/en/api.html#req
 * @param res https://expressjs.com/en/api.html#res
 */
export const helloWorld = (req, res) => {
  res.send('Hello, World!');
};

Observe error:

Provided module can't be loaded.
Is there a syntax error in your code?
Detailed stack trace: Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: esmtestff/index.js
require() of ES modules is not supported.

Solution

Here’s the rough solution I think, after prototyping a bit:

• loader.js#getUserFunction:
  • Await const functionModulePath = await getFunctionModulePath(codeLocation);
  • loader.js#getFunctionModulePath
    • We need to determine if the user code is a module or cjs.
      • if module, await import(codeLocation); where codeLocation is full file (including index.js part).
      • else, require.resolve(codeLocation), normal require
• index.js: We need to async/await getUserFunction:
  • https://github.com/GoogleCloudPlatform/functions-framework-nodejs/blob/master/src/index.ts#L99-L104

CC: @bcoe

[neilstuartcraig]

Just adding my +1 to this as it’s currently preventing me using ES modules in Cloud Functions (not firebase). I’d be happy to contribute if that’s useful.

[mbleigh]

Hey folks, just wanted to provide a nudge and a backlink to https://github.com/firebase/firebase-tools/issues/2994 – on the Firebase side we have 50+ developers 👍 requesting ESM support. We can’t add it for Firebase until it gets added for FF, so if it’s possible to make progress that would be great for our users!