Support ESM

[grant]

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

[bcoe]

@grant it's possible to build a dual-mode module, I just finished doing this for yargs-parser.

This might be worth thinking about for the functions framework.

[grant]

Alright. So I have a prototype of using dynamic imports in ESM with what I think would work for the FF implementation:

index.js

const USER_FUNCTION = 'myFunc'
const USER_FILE = './foo.js'

async function run() {
  const myFile = await import(USER_FILE);

  const res = myFile[USER_FUNCTION]();
  console.log(res);
}
run();

foo.js

export const myFunc = () => 3;

{
  "name": "dynamic-import",
  "main": "index.js",
  "type": "module",
  "scripts": {
    "start": "node ."
  }
}

You got to be pretty careful with how you load your file.

[mesqueeb]

@grant isn't "exports" Better than "main" in package.json for esm?

[grant]

@grant isn't "exports" Better than "main" in package.json for esm?

I don't think the FF user needs to provide module exports like that. Maybe provide an example if you think so?

This case is very different than most modules that support ESM. The FF loads the user's code which can be a ESM, we don't use the FF itself as a module/library (it's a binary).

[mbleigh]

Hey folks, just wanted to provide a nudge and a backlink to firebase/firebase-tools#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!

[bcoe]

@mbleigh @grant the approach of using dyamic imports seems pretty smart, perhaps we could start with this being something that users opt into, with a slightly modified start script?

Test with the folks who are excited for this feature in firebase, then at some point in the future, make it the default behavior?

[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.

[koistya]

This feature stopped working today (or, yesterday):

To load an ES module, set "type": "module" in the package.