【toggleclass】
<!DOCTYPE html>
<html>
<head>
<script type='text/javascript'
src='http://code.jquery.com/jquery-1.7.1.js'></script>
<style type='text/css'>
.first {
color: blue;
}
.second {
color: red;
}
</style>
<script type='text/javascript'>
$(window).load(function(){
$('#foo').click(function() {
$(this).toggleClass('first second');
});
});
</script>
</head>
<body>
<button id="foo" class="first">Click Me, Watch My Color Change</button>
</body>
</html>
