index.html

<form>
  <input name="item">
  <button type="submit">Add Item</button>
</form>
<ul id="todo-items">
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
</ul>

<script>
    // Now some unobtrusive javascript:

    $('form').submit(function(e) {
        e.preventDefault();
        var content = $('form').find('input').val());
        $("#todo-items").append($('<li></li>').text(content));
    })
</script>