How to bind JavaScript callback in stable 1.1.1 Dart and bind Dart callback in JavaScript (Dart2Js2Dart)?

Question

I want to write some Dart function "oKey" which calls JavaScript function "jsOnKey" (with success or exception too since cannot predict).

Next I want that JavaScript function "onKey" will call Dart function "callbackFromJs" to return control to Dart again (with success or exception).

Can you help me with this full flow - please assume SUCCESS or EXCEPTION on each border - I can not rely on 3rd party code - DART 2 JS 2 DART?

---

To make more context to this general question I put example code.

import 'dart:html';

void onKey(Event event) {
  // I want to call something in javascript
  // function callbackFromDart () { 
  //  /* something */; 
  //  /* call callbackJs in Dart - return control to dart */
  // }
}

void callbackFromJs() {
  // It should be called from JavaScript
}

void main() {
  InputElement nameElement = querySelector('input[name=name]');
  nameElement..placeholder = 'Enter text'
      ..onKeyUp.listen(onKey);

  InputElement descriptionElement = querySelector('input[name=description]');
  descriptionElement..placeholder = 'Enter text'
    ..onKeyUp.listen(onKey);
}

Answer 1

First have a look at Using JavaScript from Dart.

For your case you can simply pass callbacks to handle what you call Js 2 Dart :

import 'dart:js' as js;

void onKey(Event event) {
  onSuccess() {
    // Dart callback called from Js
  }
  onError() {
    // Dart callback called from Js
  }

  // assuming your js function takes 2 callbacks as parameters
  try {
    // in JS : function a() { throw "throw from js"; }
    js.context.callMethod('myTopLevelFunction', [onSuccess, onError]);
  } 
  catch (e) {
    print('js error catch on Dart side : $e');
  }
}

The Dart exceptions can be catch with the same kind of code on Js side.