return errors instead

packages/webview_flutter/webview_flutter_wkwebview/ios/Classes/FWFWebViewHostApi.m

@@ -170,7 +170,6 @@ - (void)evaluateJavaScriptForWebViewWithIdentifier:(nonnull NSNumber *)identifie
       evaluateJavaScript:javaScriptString
        completionHandler:^(id _Nullable result, NSError *_Nullable error) {
          id returnValue = nil;
-         FlutterError *flutterError = nil;
          if (!error) {
            if (!result || [result isKindOfClass:[NSString class]] ||
                [result isKindOfClass:[NSNumber class]]) {
@@ -183,12 +182,10 @@ - (void)evaluateJavaScriptForWebViewWithIdentifier:(nonnull NSNumber *)identifie
              returnValue = [result description];
            }
          } else {
-           flutterError = [FlutterError errorWithCode:@"FWFEvaluateJavaScriptError"
-                                              message:@"Failed evaluating JavaScript."
-                                              details:FWFNSErrorDataFromNSError(error)];
+           returnValue = FWFNSErrorDataFromNSError(error);
          }
 
-         completion(returnValue, flutterError);
+         completion(returnValue, nil);
        }];
 }
 

packages/webview_flutter/webview_flutter_wkwebview/lib/src/web_kit_webview_widget.dart

@@ -328,20 +328,21 @@ class WebKitWebViewPlatformController extends WebViewPlatformController {
 
   @override
   Future<void> runJavascript(String javascript) async {
-    try {
-      await webView.evaluateJavaScript(javascript);
-    } on PlatformException catch (exception) {
-      // WebKit will throw an error when the type of the evaluated value is
-      // unsupported. This also goes for `null` and `undefined` on iOS 14+. For
-      // example, when running a void function. For ease of use, this specific
-      // error is ignored when no return value is expected.
-      // TODO(bparrishMines): Ensure the platform code includes the NSError in
-      // the FlutterError.details.
-      if (exception.details is! NSError ||
-          exception.details.code !=
-              WKErrorCode.javaScriptResultTypeIsUnsupported) {
-        rethrow;
-      }
+    final Object? result = await webView.evaluateJavaScript(javascript);
+    // WebKit will throw an error when the type of the evaluated value is
+    // unsupported. This also goes for `null` and `undefined` on iOS 14+. For
+    // example, when running a void function. For ease of use, this specific
+    // error is ignored when no return value is expected.
+    if (result is NSError &&
+        result.code == WKErrorCode.javaScriptResultTypeIsUnsupported) {
+      return;
+    } else if (result is NSError) {
+      throw PlatformException(
+        code: 'runJavascript_failed',
+        message: 'Failed running JavaScript',
+        details:
+            "JavaScript string was: '$javascript'\n${result.localizedDescription}",
+      );
     }
   }
 
@@ -353,6 +354,13 @@ class WebKitWebViewPlatformController extends WebViewPlatformController {
         'Result of JavaScript execution returned a `null` value. '
         'Use `runJavascript` when expecting a null return value.',
       );
+    } else if (result is NSError) {
+      throw PlatformException(
+        code: 'runJavascriptReturningResult_failed',
+        message: 'Failed running JavaScript',
+        details:
+            "JavaScript string was: '$javascript'\n${result.localizedDescription}",
+      );
     }
     return result.toString();
   }

packages/webview_flutter/webview_flutter_wkwebview/test/src/web_kit_webview_widget_test.dart

@@ -6,7 +6,6 @@ import 'dart:math';
 import 'dart:typed_data';
 
 import 'package:flutter/material.dart';
-import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:mockito/annotations.dart';
 import 'package:mockito/mockito.dart';
@@ -724,15 +723,15 @@ void main() {
           (WidgetTester tester) async {
         await buildWidget(tester);
 
-        when(mockWebView.evaluateJavaScript('runJavaScript'))
-            .thenThrow(PlatformException(
-          code: '',
-          details: const NSError(
-            code: WKErrorCode.javaScriptResultTypeIsUnsupported,
-            domain: '',
-            localizedDescription: '',
+        when(mockWebView.evaluateJavaScript('runJavaScript')).thenAnswer(
+          (_) => Future<Object?>.value(
+            const NSError(
+              code: WKErrorCode.javaScriptResultTypeIsUnsupported,
+              domain: '',
+              localizedDescription: '',
+            ),
           ),
-        ));
+        );
         expect(
           testController.runJavascript('runJavaScript'),
           completes,