Flutter Web, wasm support fix

lib/excel.dart

@@ -7,6 +7,7 @@ import 'package:collection/collection.dart';
 import 'package:equatable/equatable.dart';
 import 'package:xml/xml.dart';
 import 'src/web_helper/client_save_excel.dart'
+    if (dart.library.js_interop) 'src/web_helper/wasm_web_save_excel_browser.dart'
     if (dart.library.html) 'src/web_helper/web_save_excel_browser.dart'
     as helper;
 

lib/src/web_helper/wasm_web_save_excel_browser.dart

@@ -0,0 +1,37 @@
+import 'dart:js_interop';
+import 'dart:typed_data';
+
+import 'package:web/web.dart';
+
+class SavingHelper {
+  static List<int>? saveFile(List<int>? val, String fileName) {
+    if (val == null) {
+      return null;
+    }
+
+    // Create Uint8List
+    final uint8List = Uint8List.fromList(val);
+
+    // Convert to JS object properly
+    final jsData = uint8List.toJS;
+
+    // Create blob
+    final blob = Blob(
+        [jsData].toJS,
+        BlobPropertyBag(
+            type:
+                'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'));
+
+    final url = URL.createObjectURL(blob);
+    final anchor = HTMLAnchorElement()
+      ..href = url
+      ..download = fileName;
+
+    document.body?.append(anchor);
+    anchor.click();
+    anchor.remove();
+    URL.revokeObjectURL(url);
+
+    return val;
+  }
+}