Guess.dart

import 'dart:html';

void main() {
  final ButtonElement button = querySelector('button');
  final InputElement input = querySelector('input');
  
  button.onClick
    .take(4)
    .where((event) => input.value == 'banana')
    .listen(
      (event) => print('You got it!'),
      onDone: () => print('Nope bad guesses.')
    );
  
}

guessButton.html

<h4>Guess the word</h4>
<input />
<button>Guess</button>