<!DOCTYPE html>
<html>
  <head>
    <title>Knockout</title>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=770" />
    <script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.4.0/knockout-min.js"></script>
  </head>

  <body>
    <form action="https://httpbin.org/post" method="post">
      <div class="inputs" data-bind="foreach: items">
        <div>
          <label>Name</label>
          <input type="text" name="name" autofocus data-bind="value: name, event: { change: $parent.addField }" />
        </div>
      </div>

      <div>
        <button>Save</button>
      </div>
    </form>

    <script src="knockout.js"></script>
  </body>
</html>

<!DOCTYPE html>
<html>
  <head>
    <title>Knockout</title>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=770" />
    <script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.4.0/knockout-min.js"></script>
  </head>

  <body>
    <form action="https://httpbin.org/post" method="post">
      <div class="inputs" data-bind="foreach: items">
        <div>
          <label>Name</label>
          <input type="text" name="name" autofocus data-bind="textInput: name, event: { keyup: $parent.addField }" />
        </div>
      </div>

      <div>
        <button>Save</button>
      </div>
    </form>

    <script src="knockout.js"></script>
  </body>
</html>

Add blank field as the user types
Add blank field as the user types
