igx-calendar Displays Week 53 Instead of Week 1 for Jan 1, 2025 (ISO 8601 Violation)

[fexxdev]

🐞 Bug Report

Description

The igx-calendar component displays the incorrect ISO week number for January 1st, 2025.

Specifically, the calendar labels the first week of January 2025 as Week 53, when according to the ISO 8601 standard, it should be Week 1.

This misalignment causes confusion and could result in incorrect data input or synchronization issues with systems relying on ISO-standard week numbering.

Note: January 1, 2025, is incorrectly labeled as part of Week 53. It should be Week 1.

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🔧 igniteui-angular version

• Tested with: igniteui-angular@18.x.x and igniteui-angular@19.x.x

🌐 Browser

• Chrome (version tested: latest)
• Brave (version tested: latest)

🧪 Angular Version

• Angular 18
• Angular 19

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Steps to Reproduce

1. Use the igx-calendar component in an Angular 18 or 19 project.
2. Open the calendar popup.
3. Navigate to January 2025.
4. Observe the week number shown for January 1st.

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❌ Actual Result

• The calendar shows Week 53 for Wednesday, January 1st, 2025.

✅ Expected Result

• The calendar should show Week 1 according to ISO 8601 rules, where:
  • The first week of the year is the one that contains the first Thursday of the year (or January 4th).
  • Weeks start on Monday.

Alternatively, the component should offer a configuration option to switch between US week numbering and ISO 8601 week numbering.

[simeonoff]

Duplicate of #15399