Tryit Editor v1.8

Source Code:

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("#btn1").click(function(){
    $("#test1").text(function(i,origText){
      return "Old text: " + origText + " New text: Hello world! (index: " + i + ")"; 
    });
  });

  $("#btn2").click(function(){
    $("#test2").html(function(i,origText){
      return "Old html: " + origText + " New html: Hello <b>world!</b> (index: " + i + ")"; 
    });
  });

});
</script>
</head>

<body>
<p id="test1">This is a <b>bold</b> paragraph.</p>
<p id="test2">This is another <b>bold</b> paragraph.</p>
<button id="btn1">Show Old/New Text</button>
<button id="btn2">Show Old/New HTML</button>
</body>
</html>

Result:

W3Schools.com - Try it yourself

Edit the code above and click "Submit Code" to see the result.