jquery Add and Remove Classes?

I need a script that adds a 2 to the end of a class in a div with the id .sideboxtopleft on clicking of a link with the id of posts.

<script>
    $(".posts").click(function () {
      if ($('.sideboxtopleft').is('#sideboxtopleft2')) {
          $('.sideboxtopleft').removeClass('2');
      }
      else{
          $('.sideboxtopleft').addClass('2');
      }
    });
</script>

<div id="sideboxtopleft" class="sideboxtopleft">
<a href="#post" id="posts"><h3>R开发者_高级运维ECENT POSTS <div id="arrow" class="arrow"></div></h3></a>
</div>
<div id="sideboxtopright" class="sideboxtopright">
<a href="#comments" id="comments"><h3>RECENT COMMENTS <div id="arrow" class="arrow2"></div></h3></a>
</div>

However it doesn't seem to want to work properly. Any help?

---

You can do it using .toggleClass() like this:

$(".posts").click(function () {
  $('.sideboxtopleft, .sideboxtopleft2').toggleClass('sideboxtopleft sideboxtopleft2');
});

All of the class methods add, remove, or toggle entire classes, they don't append/remove part of a class name. Though the above code works, it isn't the most ideal solution, a multi-class selector in CSS is probably a better approach, like this:

.sideboxtopleft { color: black; }
.sideboxtopleft.on { color: red; }

Then you could just toggle the on class, like this:

$(".posts").click(function () {
  $('.sideboxtopleft').toggleClass('on');
});

---

Why not just add a new class to tag?

<div id='foo' class='sideboxtopleft two'>