Package subpath './package.json' is not defined by "exports" in /Users/xxx/my_repo/node_modules/cesium/package.json

[rapha-opensource]

This is Cesium installed via npm and integrated in a Svelte/Sapper route.

1. npm install cesium
2. Add a Svelte page to a Sapper basic demo app for the route /cesium which will load a basic Cesium Viewer.
3. run npm run dev

The Svelte page

<script>
    import { onMount } from 'svelte'
    import "cesium/Build/Cesium/Widgets/widgets.css" // <= the first cesium import will cause the error !

    onMount(async () => {
        window.CESIUM_BASE_URL = 'http://localhost:3000/'
        const { Viewer } = await import('cesium')
        var viewer = new Viewer('cesiumContainer')
    })
</script>

<style>
    #cesiumContainer {
        width: 100%;
        height: 100%;
        margin: 0;
        padding: 0;
        overflow: hidden;
    }
</style>

<svelte:head>
    <title>Cesium Demo</title>
</svelte:head>
<div id="cesiumContainer"></div>

The error message

Package subpath './package.json' is not defined by "exports" in /Users/xxx/repos/my_repo/node_modules/cesium/package.json

Workaround

Delete the exports field in node_modules/cesium/package.json.
Re-launch npm run dev.

[mramato]

@rapha-opensource I would recommend you ask about this on https://community.cesium.com since no one on the Cesium team uses Svelte. Also, we use GitHub for confirmed bugs and feature tracking so it's always better to start there first anyway unless you are 100% sure of a bug.

exports is required for NodeJS compatibility, it was introduced in #8659. There's nothing non-standard about Cesium's behavior here so the problem is most likely on the svelte side (or whatever build tool you are using with it).

If you find out more information that points to something Cesium is doing wrong, please let us know and we can re-open the issue.

[wallw-teal]

This is an issue on more than just Svelte, as many bundler plugins check for config in package.json (react-native, etc.). The fix is not to remove the exports config, but to modify it to also contain ./package.json as was done in this commit.

I recommend re-opening and I'll be happy to add a PR.

[kring]

Lots of tools need to require.resolve package.json, and in the latest versions of node.js it's impossible to do in a package with exports unless the package.json is explicitly exported. There's lots of discussion about this here:
nodejs/node#33460

But in the short term, I believe adding package.json to exports is a safe and effective solution. I'm going to re-open this, and I think we'd be happy to take a PR for it @wallw-bits.