evalJavascript inconsistent between Android and iOS.

[manujbahl]

the response from evalJavascript on Android is adding a set of " at the beginning and end of the returned string.

iOS response - xyz
android response - "xyz"

[va-andrew]

+1 for this issue. iOS also has weird behavior like returning 1 for true, while Android is more typical by returning a JSON string of the result. I've been using the following to retrieve an object from an evalJavascript() statement, but it would be nice to have something less hacky/more official:

bool jsRequiresStringify;
Future evalAndParseJS(FlutterWebviewPlugin plugin, String expr) async {
  if (jsRequiresStringify == null) {
    final String boolTest = await plugin.evalJavascript('true');
    final String intTest = await plugin.evalJavascript('0');
    final String stringTest = await plugin.evalJavascript('"hello"');
    if ((boolTest == 'true') && (intTest == '0') && (stringTest == '"hello"')) {
      // Android
      jsRequiresStringify = false;
    } else if ((boolTest == '1') && (intTest == '0') && (stringTest == 'hello')) {
      // iOS
      jsRequiresStringify = true;
    } else {
      // Unknown behavior
      jsRequiresStringify = true;
    }
  }
  final String fullExpr = jsRequiresStringify ? 'JSON.stringify($expr)' : expr;
  final String resultStr = await plugin.evalJavascript(fullExpr);
  try {
    return jsonDecode(resultStr);
  } catch(e) {
    print('jsonDecode error! $e');
    return null;
  }
}

[lejard-h]

Indeed iOS has a strange behavior on this. How do you determine if the 1 you get, is the result of a boolean or number ?

For your function, you can use Platform.isIOS and Platform.isAndroid instead of testing evalJavascript.

I could add it to the plugin but it does not seem to be a good solution for now.

[ASemeniuk]

The problem actually has greater scope than flutter_webview_plugin. It seems that JavaScriptChannel behaves differently on these platforms. In my projects I am forced to use hacks as ones suggested above.