Dart Learning: Simple "E-mail" validator with Stream

form.html

<h4>Enter your email</h4>
<input />
<div style="color: red;"></div>

SimpleValidEmail.dart

import 'dart:html';
import 'dart:async';

void main() {
  final InputElement input = querySelector('input');
  final DivElement div = querySelector('div');
  
  final validateEmail = new StreamTransformer.fromHandlers(
    handleData: (inputValue, sink) {
      if (inputValue.contains('@')) {
        sink.add(inputValue);
      } else {
        sink.addError('Enter a valid email');
      }
    }
  );
  
  
  input.onInput
    .map((dynamic event) => event.target.value)
    .transform(validateEmail)
    .listen(
      (inputValue) => div.innerHtml = '',
      onError: (err) => div.innerHtml = err   
    );
}