<script src="https://libs.baidu.com/jquery/1.10.2/jquery.min.js">
$(this).animate({fontSize:"+=3px"});
$(this).animate({letterSpacing:"+=2px"});
$(document).ready(function(){
$("body").delegate("p","click",changeSize);
$("body").delegate("p","click",changeSpacing);
$("button").click(function(){
$("body").undelegate("p","click",changeSize);
<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
<p>Click any p element to increase size and letterspacing.</p>
<button>Remove the event handler changeSize() for all p elements</button>