getStyleModel(id) function throws runtime errors because some expected properties are missing.

[PaulChinta7]

🐛 Bug Report

Description

File:
exceljs/lib/xlsx/xform/style/styles-xform.js

Function:
getStyleModel(id)

When reading certain corrupted or malformed Excel files, the getStyleModel(id) function throws runtime errors because some expected properties are missing.

Specifically:

• this.model does not always contain a styles property, so:

  this.model.styles[id];

  throws TypeError: Cannot read properties of undefined.

• this.index does not always contain a model property, so:

  this.index.model[id];

  also throws a TypeError.

Because of this, execution stops instead of handling the missing style gracefully.

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Steps To Reproduce

I cannot share the original file because it contains sensitive work data.

The issue occurs when using WorkbookReader to stream-read a file:

while await (const row of workbookReader) {
  // process row
}

While processing rows, the reader internally calls getStyleModel(id), which throws when styles or model is undefined.

Basic workbook usage works normally:

const wb = new ExcelJS.Workbook();
const ws = wb.addWorksheet('XYZ');

ws.getCell('A1').value = 7;
expect(ws.getCell('A1').value).to.equal(7);

The issue specifically appears when reading certain corrupted files.

---

Expected Behavior

The library should not crash when style metadata is missing or malformed.

Instead, it should:

• Safely handle missing styles or model properties
• Return null or a default value
• Continue processing without throwing an uncaught exception

---

Possible Solution

Add defensive checks before accessing nested properties:

// if the style doesn't exist return null
const style = this.model && this.model.styles ? this.model.styles[id] : null;
if (!style) return null;

// have we built this model before?
let model = this.index && this.index.model ? this.index.model[id] : null;
if (model) return model;

This would prevent runtime errors when processing corrupted or incomplete files and allow the reader to fail gracefully instead of terminating execution.