TypeError: N.startsWith is not a function when parsing Microsoft Office 365 ICS files

[tkak]

Thank you for developing and maintaining this project! I appreciate all your hard work.

I've encountered an issue when processing calendar data, which seems to be related to the interaction between Microsoft Outlook generated iCal files and how node-ical parses them. While I suspect the root cause might lie with either Microsoft's iCal generation or node-ical's parsing of specific non-standard (or less common) iCal properties, I'm reporting it here as it affects the functionality of this project.

Problem:

The node-ical library fails to parse ICS files from Microsoft Office 365 with the error TypeError: tz.startsWith is not a function at line 265 in ical.js.

Error Details:

plugin:ics:27 Error processing calendar Outlook: TypeError: N.startsWith is not a function
getEvents @ plugin:ics:27
await in getEvents
editorCallback @ plugin:ics:31
e.addCommand.e.mobileOnly.Gl.isMobile.e.checkCallback @ app.js:1
sQ @ app.js:1
t.onChooseItem @ app.js:1
t.onChooseSuggestion @ app.js:1
t.selectSuggestion @ app.js:1
e.useSelectedItem @ app.js:1
(anonymous) @ app.js:1
e.handleKey @ app.js:1
e.onKeyEvent @ app.js:1

Root Cause:

Microsoft Office 365 uses timezone names with spaces like TZID=Tokyo Standard Time in RECURRENCE-ID fields. The library expects the tz parameter to be a string, but it receives a different data type.

• https://feedbackportal.microsoft.com/feedback/idea/f040bead-3478-f011-95f3-7c1e52d941f8

Sample ICS File:

The problematic ICS contains entries like:
RECURRENCE-ID;TZID=Tokyo Standard Time:20240924T163000

[muness]

Hi @tkak - thanks for digging into this and helping me understand what's going on. This has come up before (#145, e.g.) but I didn't understand what might be happening. An update to deps even fixed #145 without me doing anything else, which might actually match the issue(s) you see.

The link you added identified the root cause: Microsoft Outlook uses Windows timezone names rather than IANA, and includes VTIMEZONE definitions in shared calendar .ics files, but events like those in 'Brussels, Copenhagen, Madrid, Paris' are shown as "Romance Standard Time" without the corresponding VTIMEZONE definition being included in the .ics file.

What I've Done

• Found the official Unicode CLDR Mappings: Instead of hardcoding timezone mappings, I've integrated the official Windows to IANA timezone mappings at https://github.com/unicode-org/cldr/blob/main/common/supplemental/windowsZones.xml
• Added a script to generate Timezone Mappings: This covers all Windows timezone names including:
  • "Romance Standard Time" → "Europe/Paris"
  • "Tokyo Standard Time" → "Asia/Tokyo"
  • "Eastern Standard Time" → "America/New_York"
• Graceful Error Handling: The plugin now catches the tz.startsWith is not a function error and automatically preprocesses the ICS content to replace Windows timezone names with IANA equivalents, then retries parsing. Hopefully that fixes the issue

How It Works

When the node-ical library fails with a timezone-related error:

1. The plugin catches the error and logs a warning
2. Preprocesses the ICS content to map Windows → IANA timezone names
3. Retries parsing with the corrected content
4. Logs success and continues normally

Hopefully this means zero breaking changes for existing users, while providing robust compatibility with Microsoft Office 365 calendars.

Maintainability

The timezone mappings can be updated anytime by running:

npm run update-timezones

This fetches the latest mappings from Unicode CLDR and regenerates the timezone files.

Would love to hear if 1.11.0 resolves the issues you have been experiencing with Microsoft Office 365 calendars! 🤞

[muness]

Hi @tkak - would love your feedback, did 1.11.0 help? Thank you!

[tkak]

Hi @muness, thank you so much for checking this. I tried 1.12.0, but it's still not working.

Error processing calendar Microsoft 365 Calendar: Error: ICS parsing failed: u.startsWith is not a function. Preprocessing also failed: u.startsWith is not a function

obsidian.md-1759533465997.log