input

index.html

<div id='root'>
</div>

main.dart

import 'dart:html' as html;

void main() {
  var input = html.document.createElement('input');
  var output = html.document.createElement('p');

  html.querySelector('#root').append(input);
  html.querySelector('#root').append(html.document.createElement('br'));
  html.querySelector('#root').append(output);

  input.onInput.listen(
      (e) => output.innerText = ((e.currentTarget as html.InputElement).value));
}