Please provide a CJS export.

[dwjohnston]

Currently (v 19.4.1) the imported package looks like this:

//package.json 
    "type": "module",
    "exports": {
        "types": "./index.d.ts",
        "default": "./index.js"
    },
    "sideEffects": false,
    //snip
    "files": [
        "index.js",
        "index.d.ts",
        "src/**/*.js",
        "src/**/*.d.ts"
    ],

//index.js

import useLocalStorageState from './src/useLocalStorageState.js';
export default useLocalStorageState;

The problem with this is that despite ESM being generally well supported, a lot of tooling still has difficulty with it.

For example, Jest has limited ESM support.

I have a reproduction here demonstrating difficulty using this package with Jest

https://github.com/dwjohnston/localstorage-repro

Relevant other resources:

https://jestjs.io/docs/ecmascript-modules

https://stackoverflow.com/questions/68520619/jest-typescript-with-es-module-in-node-modules-error-must-use-import-to-load-e

Suggested solution

Package json looks like this:

  "exports": {
    ".": {
      "require": "./index.cjs", // CJS
      "import": "./index.mjs", // ESM
      "types": "./index.d.ts" // types
    }
  }

[dwjohnston]

Incase anyone needs it - adding this to your jest.config might solve this issue for you:

  transformIgnorePatterns: ['node_modules\\/(?!use-local-storage-state\\/)'],

ie. it's telling jest to ignore all node modules, but not this one - please transpile it.

[astoilkov]

This package was supporting CJS before but I removed it — https://github.com/astoilkov/use-local-storage-state/issues/61.

Here's also a related discussion on the topic from a few days ago — https://github.com/astoilkov/p-signal/issues/1.

I had some issue maintaining and fixing stuff around CJS so I decided to drop it. Also, there are sindresorhus, wooorm, and other popular open-source contributors that are advocating for move to ESM and I kinda support it.

For example, sindresorhus modules are ESM only and his packages are downloaded 30B+ times a month. I feel like if this is the case, people are able to successfully make their tooling work.

Here's the link that sindresorhus discusses the ESM only move — Pure ESM package.

Another point to make is this chart — https://x.com/wooorm/status/1829180747070181793 — where dual (ESM and CJS) support is less common than ESM only.

[dwjohnston]

Alright, you might have changed my mind here.

The main time I encounter this, is with Jest, but the fix for it is easy enough.

(Well, we'll see, maybe I should retain a list of various toolings that don't behave nicely with ESM).

[astoilkov]

Thanks for thinking about this and continuing with the discussion!

What do you want us to do here? Are you ok with closing this issue and the associated PR?

[dwjohnston]

Sure, let's close it. What I'm going to do is maintain my own list for my own reference of scenarios where untranspiled ESM in packages causes issues.

[dwjohnston]

For posterity - here's the list: https://blacksheepcode.com/posts/list_of_tooling_that_does_not_play_nicely_with_esm :)