Adopt upstream PR #2956: Fix excelToDate() for non-numeric values

[protobi-pieter]

Summary

Adopt upstream PR exceljs#2956 to fix handling of non-numeric values in excelToDate().

Currently, when a non-numeric value is passed to excelToDate() (e.g., when a cell has date formatting but contains text), it returns "Invalid Date" which gets converted to NaN and causes Excel to show warnings when opening the file.

Upstream PR

• PR: Fix the return value from dateToExcel() when it's passed a non-numeric value. exceljs/exceljs#2956
• Author: @davepuchyr
• Created: 2025-08-12
• Status: Open in upstream

Changes

File modified:

• lib/utils/utils.js - Add validation check in excelToDate() (1 line)

Total: 1 addition, 0 deletions

Bug Description

When a cell has date formatting but contains a non-numeric value, excelToDate() tries to convert it and returns "Invalid Date", which persists as NaN in the Excel file.

Current behavior:

excelToDate(v, date1904) {
  const millisecondSinceEpoch = Math.round((v - 25569 + ...) * 24 * 3600 * 1000);
  return new Date(millisecondSinceEpoch);  // Returns Invalid Date for non-numeric v
}

Fixed behavior:

excelToDate(v, date1904) {
  if (!Number.isFinite(v)) return v;  // Return original value if not numeric
  const millisecondSinceEpoch = Math.round((v - 25569 + ...) * 24 * 3600 * 1000);
  return new Date(millisecondSinceEpoch);
}

Value Proposition

• Low Risk - Single line validation check
• Bug Fix - Prevents Excel warnings on file open
• User Experience - Eliminates annoying error popups

Testing Plan

• Apply changes from upstream PR
• Run existing test suite
• Verify non-numeric values don't cause Invalid Date

[protobi-pieter]

✅ Complete

This issue was successfully resolved in commit daa210b on November 7, 2025, and closed on November 10, 2025.

Changes Applied

The fix from upstream PR #2956 was applied to lib/utils/utils.js:

Before:

excelToDate(v, date1904) {
  const millisecondSinceEpoch = Math.round((v - 25569 + (date1904 ? 1462 : 0)) * 24 * 3600 * 1000);
  return new Date(millisecondSinceEpoch);  // Returns Invalid Date for non-numeric v
}

After:

excelToDate(v, date1904) {
  if (!Number.isFinite(v)) return v;  // Return original value if not numeric
  const millisecondSinceEpoch = Math.round((v - 25569 + (date1904 ? 1462 : 0)) * 24 * 3600 * 1000);
  return new Date(millisecondSinceEpoch);
}

This prevents "Invalid Date" errors when a cell has date formatting but contains a non-numeric value, eliminating Excel warnings when opening the file.

Testing

• ✅ All existing tests pass
• ✅ Code merged to master branch
• ✅ Pushed to remote repository
• ✅ Non-numeric values no longer cause Invalid Date

Checklist Status

• Apply changes from upstream PR
• Run existing test suite
• Verify non-numeric values don't cause Invalid Date