Uncaught TypeError: Cannot read property 'isHiddenDay' of undefined

I’ve created a Svelte implementation of FullCalendar and I have issues upgrading to v5.

I use rollup as my builder and a postcss plugin for the styles, and tried to follow this guide.

I try to initialize the calendar with these options:

let options = {
	initialView: 'dayGridMonth',
	plugins: [dayGridPlugin],
};

This is what I get in the browser’s console:

main.js:8102 Uncaught TypeError: Cannot read property 'isHiddenDay' of undefined
    at new DaySeriesModel (main.js:8102)
    at DayTableView.buildDayTableModel (main.js:1080)
    at DayTableView.buildDayTableModel (main.js:983)
    at DayTableView.render (main.js:1069)
    at T (preact.module.js:1)
    at g (preact.module.js:1)
    at j (preact.module.js:1)
    at T (preact.module.js:1)
    at g (preact.module.js:1)
    at T (preact.module.js:1)

• This is the component implementation.
• I can’t actually upload a live demo since I need a postcss plugin to handle the css-in-js.

[arshaw]

I have some more insight into the problem. For some reason, when installing @fullcalendar/core and the plugins, npm is not deduping @fullcalendar/common. Sometimes there are multiple copies of it, nested within fullcalendar’s other dependencies.

@YogliB I was able to clone your repro and reproduce the error. When I reinstalled the deps, making a new lock file, things began to work:

rm -rf node_modules package-lock.json
npm install

I’m not sure why. I bet that trick will work for others.

[irfanonk]

I have got exact the same issue,(Cannot read property ‘isHiddenDay’ of undefined) so i searched and ended up here. then I realized that there wasn’t any “@fullcalendar/timegrid”: “^5.1.0”, in my package.json even I installed with npm install @fullcalendar/timegrid. so then I installed with npm install --save @fullcalendar/timegrid (with --save) and made sure that it’s in package.json dependencies, that eventually solved problem.