Dispatching custom events example for Dart Web projects

index.html

<input type="text" />

main.dart

import 'dart:html';

void main() {
  final input = querySelector('input');
  
  input.onKeyPress.listen((data) {
    final customKeypress = CustomEvent('keypress', detail: {
      'keyCode': data.keyCode,
      'charCode': data.charCode,
    });
    input.dispatchEvent(customKeypress);
  });
  
  input.on['keypress'].listen((data) {
    print('Heyyy! ${(data as CustomEvent).detail['keyCode']}');
  });
}