<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>

<div>

  <p>名字 : <input type="text" name="userName" onkeyup="test()"></p>

  <h1>Hello </h1>

</div>

function test()

{

  var userName=$("input[name='userName']").val();

  $("h1").html(userName);

 }