Switch from faux-ESM to real ESM exports

[karlhorky]

Reporting an issue

Thank you for taking an interest in rrule! Please include the following in
your report:

• Verify that you've looked through existing issues for duplicates before
  creating a new one
• Code sample reproducing the issue. Be sure to include all input values you
  are using such as the exact RRule string and dates.
• Expected output
• Actual output
• The version of rrule you are using 2.7.0
• Your operating system macOS Monterey 12.4
• Your local timezone (run $ date from the command line
  of the machine showing the bug)

The "module" field in package.json is non-official, and not a real ESM specification of npm: https://stackoverflow.com/a/42817320/1268612

Switching away from "module" to use the "exports" and "type": "module" fields in the package.json would allow for better compatibility with ESM, everywhere it is used.

You may even consider making it a pure ESM package, as mentioned here: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c

Expected output (see "type" and "exports" fields):

$ cat node_modules/rrule/package.json
{
  "name": "rrule",
  "version": "2.7.0",
  ...
  "main": "dist/es5/rrule.js",
  "type": "module",
  "exports": "./dist/esm/src/index.js",
  "types": "dist/esm/src/index.d.ts",
  ...
}

Actual output (see the outdated faux-ESM "module" field):

$ cat node_modules/rrule/package.json
{
  "name": "rrule",
  "version": "2.7.0",
  ...
  "main": "dist/es5/rrule.js",
  "module": "dist/esm/src/index.js",
  "types": "dist/esm/src/index.d.ts",
  ...
}

[davidgoli]

Thanks for the suggestion. I don't think we're ready to abandon cjs users at this point, especially considering how new ESM is to Node itself, but I would like to improve the ESM support. What do you think about a solution like the one outlined here: https://redfin.engineering/node-modules-at-war-why-commonjs-and-es-modules-cant-get-along-9617135eeca1

[karlhorky]

Maybe it would work, I've heard some (rare) accounts of projects providing both ESM and CJS successfully. Any kind of improvement would be great! 👍

[davidgoli]

Please take a look at the latest (2.7.1) and let me know how it's working for you now

[karlhorky]

@davidgoli thanks for the new version!

rrule is still not published as ESM.

Importing and using rrule in the following file (import copied from the rrule readme) leads to an error.

index.mjs

import { RRule } from 'rrule';

console.log(RRule);

The error is this below:

$ node index.mjs
file:///Users/k/p/ical-move-events/index.mjs:1
import { RRule } from 'rrule';
         ^^^^^
SyntaxError: Named export 'RRule' not found. The requested module 'rrule' is a CommonJS module, which may not support all module.exports as named exports.
CommonJS modules can always be imported via the default export, for example using:

import pkg from 'rrule';
const { RRule } = pkg;

    at ModuleJob._instantiate (node:internal/modules/esm/module_job:124:21)
    at async ModuleJob.run (node:internal/modules/esm/module_job:179:5)
    at async Loader.import (node:internal/modules/esm/loader:178:24)
    at async Object.loadESM (node:internal/process/esm_loader:68:5)
    at async handleMainPromise (node:internal/modules/run_main:63:12)

Luckily there is a workaround and it is printed out in the error message, but a lot of users will probably not notice it or not understand:

import pkg from 'rrule';
const { RRule } = pkg;

console.log(RRule);

So probably this issue should be reopened, for seamless real ESM support.

[karlhorky]

@davidgoli do you think you could reopen this issue? I think it is not resolved yet.

[karlhorky]

@davidgoli I've opened a new issue for this instead:

Superseded by #548

[JuicyZest]

Same Issue here,
import pkg from 'rrule';
const { RRule } = pkg;
This workaround resolves the module error, but gives me a RRule is not a constructor error when trying to create a new RRule object.
Anyone ever found a solution ?

[karlhorky]

@JuicyZest this issue is closed, can you copy your comment above to the current issue over here?

• Switch from faux-ESM to real ESM exports #548