AngularJS Example:

HTML

<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.12.4/jquery.js"></script>
<div ng-app>
  <form>
    <textarea rows="4" type="text" ng-model="todoText" size="30" placeholder="add new todo here">
    </textarea>
  </form>
  <h1>{{todoText || 'Hello World'}}</h1>
</div>

JavaScript

$(function() {
	$("textarea").val($("h1").text());
	$("textarea").keyup(function() {
		$("h1").text($("textarea").val());
	});
});