jquery stop executing after callback function
<p>I have a simple plugin, used for submitting form</p>

<pre><code>(function($){
    $.fn.ajaxSubmit = function(options){
        var defaults = {
            onSubmit:function(){},
        },
        o = $.extend({},defaults, options);

        return this.each(function(){
            $(this).submit(function(e){
                o.onSubmit.call(this);
                $.post(o.url,$(this).serialize() ,
                function(i){"do stuff"},'json');
                return false;
            });
        });
    }
})(jQuery);
</code></pre>

<p>And this is how I call it</p>

<pre><code>$('#commentForm').ajaxSubmit({
    onSubmit:function(){
        if($('textarea').val()==''){ "do not execute $.post"}
    }
});
</code></pre>

<p>I want to check if textarea is empty, if it is, do not proceed further down the plugin or do not execute the $.post.</p>
