evaluateJavascript method

Future<String?> evaluateJavascript(String javascriptString)

Evaluates a JavaScript expression in the context of the current page.

On Android returns the evaluation result as a JSON formatted string.

On iOS depending on the value type the return value would be one of:

• For primitive JavaScript types: the value string formatted (e.g JavaScript 100 returns '100').
• For JavaScript arrays of supported types: a string formatted NSArray(e.g '(1,2,3), note that the string for NSArray is formatted and might contain newlines and extra spaces.').
• Other non-primitive types are not supported on iOS and will complete the Future with an error.

The Future completes with an error if a JavaScript error occurred, or on iOS, if the type of the evaluated expression is not supported as described above.

When evaluating Javascript in a WebView, it is best practice to wait for the WebView.onPageFinished callback. This guarantees all the Javascript embedded in the main frame HTML has been loaded.

Implementation

Future<String?> evaluateJavascript(String javascriptString) {
  if (_settings.javascriptMode == JavascriptMode.disabled) {
    return Future<String>.error(FlutterError(
        'JavaScript mode must be enabled/unrestricted when calling evaluateJavascript.'));
  }
  if (javascriptString == null) {
    return Future<String>.error(
        ArgumentError('The argument javascriptString must not be null.'));
  }
  // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
  // https://github.com/flutter/flutter/issues/26431
  // ignore: strong_mode_implicit_dynamic_method
  return _webViewPlatformController.evaluateJavascript(javascriptString);
}