js-interop testing if javascript object has a property

Question

Is it possible to test if a javascript object contains a property?

I'm currently wrapping try/catch for each property I'd like to access. I dont think this is an efficient way to check if properties exist on the object.

Answer 1

Using try-catch is the more efficient way to check that because there's only one exchange between Dart and Js.

---

An other way could be to handle your javascript object like a Dart Map with :

import 'package:js/js.dart' as js;
import 'package:js/js_wrapping.dart' as jsw;

main() {
  final myProxy = ...;
  Map<String, dynamic> myProxyAsMap = jsw.JsObjectToMapAdapter.cast(proxy);
  Iterable<String> keys = myProxyAsMap.keys;
}

But it is less efficient to check if keys.contains("key") than to use the try-catch way. Moreover if you intensively use this keys consider to copy the List with a keys = myProxyAsMap.keys.toList(). Actually myProxyAsMap.keys is still baked by an underlying js array. The .toList() will create a real Dart List and prevent Dart-js exchanges.