Dart mapping Function as constructor with node interop

Issue

I’ve recently started with development in Dart. I need to run Dart on the node vm. Currently, I am required to create an interop to an external node module.

This module only exposes constructor functions. I am unable to find a way to create a Dart class that maps to a package.

Assuming the following node module export:

{
  Client: [Function: Client],
  Server: [Function: Server]
}

In this scenario I am trying to create a new instance of Client in my Dart workspace. I’ve created the following anonymous classes:

@JS()
@anonymous
abstract class ClientImpl {
  // ClientImpl(String, num);
  external String get host;
  external num get port;
}

@JS()
@anonymous
abstract class Module {
  ClientImpl Client(String, num);
}

Now I want to map the Module class to the node module

final Module _module = require('...');

void main() {
  final client = _module.Client('192.168...', 1234);
}

No typing errors are shown by the analyzer and Dart compiles correctly to Javascript using dart2js. Now when I run my compiled js file in the node VM I get an exception on creating a new instance of Client. It requires the new keyword. When I manually add the new keyword in the compiled js file I can properly instantiate the interop class.

I’ve also tried to use a typedef instead, but that didnt book any success at all.

typedef ClientFunc = ClientImpl Function(String, num);

I can’t find any examples online which describe my specific scenario. Is there anyone here who has had the same problem or know what I am doing wrong here?

Thanks in advance

Solution

This isn’t exactly an answer my the question, but I am using a workaround for now..

const { Client, Server } = require('...')

module.exports = {
  Client: (hostAddr, port) => new Client(hostAddr, port),
  Server: (...args) => new Server(...args)
}

Now a normal function is exposed instead of a constructor function. However, there must be a way to solve the above without having to write a proxy for it as this one.

Answered By – Shane

Answer Checked By – Jay B. (FlutterFixes Admin)