withIntCallback function
Implementation
Future<int> withIntCallback(
Function(Pointer<NativeFunction<Void Function(Int32)>>) func) async {
JSArray retVal = createBoolCallback();
var promise = retVal.toDart[0] as JSPromise<JSNumber>;
var fnPtrAddress = retVal.toDart[1] as JSNumber;
var fnPtr = Pointer<NativeFunction<Void Function(Int32)>>.fromAddress(
fnPtrAddress.toDartInt);
func(fnPtr);
final addr = await promise.toDart;
return addr.toDartInt;
}