Switch from faux-ESM to real ESM exports

[karlhorky]

Supersedes #512

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Actual output (see the outdated faux-ESM "module" field):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

---

Does version 2.7.1 fix this? Short answer: No.

Longer answer (from #512 (comment) ):

@davidgoli thanks for the new 2.7.1 version!

However, it does not resolve the issue - 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);

Demo (on Replit)

https://replit.com/@karlhorky/MotionlessUsedLoop#index.mjs

file:///home/runner/MotionlessUsedLoop/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:128:21)
    at async ModuleJob.run (node:internal/modules/esm/module_job:194:5)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:385:24)
repl process died unexpectedly: exit status 1

[ryantan]

Is this closed now? I can do import { RRule } from 'rrule'; with no issues

[karlhorky]

@ryantan are you using ES Modules with Node.js? Eg. with "type": "module" or an *.mjs file, no other transpilers / compilers like TypeScript or Babel?

If not (eg. if you're using TypeScript), then probably internally it is translating it to a version that works with your Node.js version.

I have added this Replit to the original post to demonstrate the problem:

https://replit.com/@karlhorky/MotionlessUsedLoop#index.mjs

file:///home/runner/MotionlessUsedLoop/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:128:21)
    at async ModuleJob.run (node:internal/modules/esm/module_job:194:5)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:385:24)

[eytanProxi]

Any news ?

[splurgebudget]

Same - still getting this with 2.7.2

[caioamaral]

I'm stuck here too

[karlhorky]

Workaround

Until this issue is properly resolved, here are some things that you may want to try:

My solution is working for my project, which is using tsc, tsx and vite:

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

If you're getting an error about the default export, another thing to try is the import * as pkg ... syntax:

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

[splurgebudget]

@karlhorky 's workaround didn't work for me. I was trying to reuse the same code in both Node and on the frontend (browser)... and either of the options would fail on one or the other.

Ultimately, I fixed it using dynamic import like so:

let rrule = await import("rrule");
let RRule = rrule.RRule;
if (!RRule) RRule = rrule.default.RRule;

[karlhorky]

Maybe your project is still CommonJS? You could try switching to ESM (ECMAScript Modules) by adding "type": "module" to your package.json (additional configuration may be needed).

[codingedgar]

My workarround for working with Vite on the browser and node 20 / testing was:

import * as pkg from 'rrule';
const { RRule } =  pkg.default || pkg;

In case anyone needs help.

[mognutecnologia]

I had the same scenario as @splurgebudget , where I am sharing code between frontend and backend through Npm Workspaces Monorepo.
Solved it as @codingedgar , but tweaking a bit to pass through Typescript compilation, in case it helps somebody:

import * as pkg from "rrule";
const tsIgnorePkg = pkg as any;
const { RRule } = tsIgnorePkg.default || tsIgnorePkg;

[septatrix]

For me the workarounds do not work with Nuxt.js and I either get the above error about not being able to import rrule without it or the tslib module not being found when trying the workaround (though it would even be installed - not sure however why it would need it) :/

PS: I had rrule imported in several files split across my codebase (and third party packages) so my only option was to use the build.transpile option of nuxt. However, I also needed to add tslib to the list of packages which have to be transpiled for everything to function properly. That seems to have fixed it for me.

[michaelhays]

Any chance we can get this implemented? The faux-ESM of this package has caused me quite a few headaches over the past year.

I'm happy to create a PR if I could have some assurance that this is a priority.

[JohnRPB]

I also have issues with ESM on the one hand, or webpack bundling on the other, and the fix that works for me is re-exporting from a wrapper file like this:

import * as rrule from 'rrule';

const getDefault = pkg => pkg.default; 

export const RRule = rrule.RRule || getDefault(rrule)?.RRule;

By using a closure, we avoid webpack's "no default export" error.

[septatrix]

Even though I am generally not a huge fan of forking unless the maintainer has officially abandoned/archived a project it might be time to do this here. The last commit is 6 months old, the last release was 2 years ago, and there are a bunch of unresolved PRs.

I would be happy if @jkbrzt could give a statement on whether or not he would still like to maintain and keep this project alive? Maybe also @davidgoli who seems to have contributed a decent amount.

[davidgoli]

I don't have time to maintain this project any more, and I don't have a professional use for it at the moment either. I would be happy to hand the reins to someone who is more committed than I am.