@fullcalendar/icalendar plugin seems broken?

When I try installing @fullcalendar/icalendar to import ical formats into FullCalendar in a SvelteKit app, I get the following error:

ICAL is not defined
ReferenceError: ICAL is not defined
    at node_modules/ical.js/build/ical.js (http://localhost:3000/node_modules/.vite/chunk-MWROEMAF.js?v=d2a4f7e5:9:12)
    at __require (http://localhost:3000/node_modules/.vite/chunk-B7LZDY4N.js?v=d2a4f7e5:41:44)
    at http://localhost:3000/node_modules/.vite/@fullcalendar_icalendar.js?v=d2a4f7e5:16:23

Any thoughts on a fix?

[notKamui]

@sbutler-gh @YogliB to recapitulate (so that you can put it somewhere) :

In case you want to use the fullcalendar/icalendar plugin, an issue might arise in projects where modules or strict mode are enabled (so, incidentally, with Svelte), and is caused by a dependency of fullcalendar (which is ical.js).

It is due to the fact that they assign a variable without declaring it.

A possible hotfix would be this :

• Create a postinstall.js file at the same level as your package.json, with the following content :

const fs = require('fs');

fs.readFile('node_modules/ical.js/build/ical.js', 'utf8', (err, data) => {
    if (err) {
        throw err
    } else {
        if (data.startsWith("let ICAL;")) return;
        fs.writeFile('node_modules/ical.js/build/ical.js', "let ICAL;\n" + data, (err) => {
            if (err) throw err;
        });
    }
});

• add the following run script to your package.json:

{
    "scripts": {
        "postinstall": "node postinstall"
    }
}

This will patch the library after each npm install

[sbutler-gh]

can you link a reproduction?

Here’s a repo reproducing the error (https://github.com/sbutler-gh/icalendar-bug). To reproduce:

1. Install the repository locally (git clone https://github.com/sbutler-gh/icalendar-bug.git)
2. npm run install
3. npm run dev

When I navigate to localhost:3000, the browser shows:

ICAL is not defined
ReferenceError: ICAL is not defined
    at node_modules/ical.js/build/ical.js (http://localhost:3000/node_modules/.vite/@fullcalendar_icalendar.js?v=6fbf720c:15:12)
    at __require (http://localhost:3000/node_modules/.vite/chunk-OZKD6XBJ.js?v=6fbf720c:9:44)
    at http://localhost:3000/node_modules/.vite/@fullcalendar_icalendar.js?v=6fbf720c:5124:24
    ```