Fix #3028: make getWorksheet case-insensitive to match addWorksheet

lib/doc/workbook.js

@@ -112,7 +112,9 @@ class Workbook {
       return this._worksheets[id];
     }
     if (typeof id === 'string') {
-      return this._worksheets.find(worksheet => worksheet && worksheet.name === id);
+      // Case-insensitive to match addWorksheet's uniqueness rule (and Excel itself).
+      const target = id.toLowerCase();
+      return this._worksheets.find(ws => ws && ws.name.toLowerCase() === target);
     }
     return undefined;
   }

spec/integration/issues/issue-3028-getworksheet-case-insensitive.spec.js

@@ -0,0 +1,46 @@
+const ExcelJS = verquire('exceljs');
+
+describe('github issues', () => {
+  describe('issue 3028 - workbook.getWorksheet should be case-insensitive', () => {
+    it('returns the same worksheet regardless of name casing', () => {
+      const wb = new ExcelJS.Workbook();
+      const ws = wb.addWorksheet('TestSheet');
+
+      expect(wb.getWorksheet('TestSheet')).to.equal(ws);
+      expect(wb.getWorksheet('testsheet')).to.equal(ws);
+      expect(wb.getWorksheet('TESTSHEET')).to.equal(ws);
+      expect(wb.getWorksheet('tEsTsHeEt')).to.equal(ws);
+    });
+
+    it('returns undefined for genuinely unknown names', () => {
+      const wb = new ExcelJS.Workbook();
+      wb.addWorksheet('TestSheet');
+
+      expect(wb.getWorksheet('OtherSheet')).to.equal(undefined);
+    });
+
+    it('preserves numeric id lookup', () => {
+      const wb = new ExcelJS.Workbook();
+      const ws = wb.addWorksheet('TestSheet');
+
+      expect(wb.getWorksheet(ws.id)).to.equal(ws);
+    });
+
+    it('preserves the no-arg first-worksheet shortcut', () => {
+      const wb = new ExcelJS.Workbook();
+      const ws = wb.addWorksheet('TestSheet');
+
+      expect(wb.getWorksheet()).to.equal(ws);
+    });
+
+    it('aligns getWorksheet with addWorksheet case-insensitive uniqueness', () => {
+      // addWorksheet rejects "testsheet" as a duplicate of "TestSheet";
+      // therefore getWorksheet("testsheet") must locate the existing sheet.
+      const wb = new ExcelJS.Workbook();
+      const ws = wb.addWorksheet('TestSheet');
+
+      expect(() => wb.addWorksheet('testsheet')).to.throw();
+      expect(wb.getWorksheet('testsheet')).to.equal(ws);
+    });
+  });
+});