Posting dynamic type message to Web Worker.

[ebala96]

I have written dart side post message to send dart Map to web worker postMessage.

Future<void> postMessageDynamic(int id, message) async{
    final worker = _workers[id];
    Map<String , dynamic> messageMap = message as Map<String,dynamic>;

    worker.postMessage(messageMap.toJSBox);
}

But toJsBox creates an empty object without the actual Map data I want to send.
Let me know how can I send dart Map to postMessage without using json encoding.

[srujzs]

Dart Maps are not JS types and they can not be passed directly to postMessage. In order to clone a Map into a JS object, use jsify e.g. messageMap.jsify().

[ebala96]

A follow up on js interop.

How can I define list of any type inside interop definiftion?

[srujzs]

Lists also are not JS types so they'll need to be converted to a JSArray, either through a manual conversion with List<JSAny?>.toJS or using jsify. The appropriate type for a JSArray of any type is JSArray<JSAny?>.

[ebala96]

I am sending dartMap.jsify() to web workers and getting back JS object from web worker.
On receiving back from web worker I do a message.data.dartify() and convert it into Map<String, dynamic> using
Map<String, dynamic>.from(message.data.dartify() as Map)

I am expecting my Map data to be Map<String, List<String>>
Since dartify map conversion mentioned above which I am doing gives Map<String, List<Object?>>, I have to do one more iteration in List to do a List conversion.

What is the better way to type convert this?

[srujzs]

Right, the generic cast will fail because the type parameters are just Object?. JS arrays and objects are allowed to contain values of different types, and therefore the resulting generics are Object?. If you control the code that iterates through the map you can use the cast function to do the cast without having to iterate over the list e.g.

final map = (original.jsify().dartify() as Map).cast<String, List>();
for (final key in map.keys()) {
  final list = map[key].cast<String>();
  ...
}

If you want to avoid that extra iteration, you can manually convert the map yourself using interop (which will be faster), but that'll require more code.