1. Create a private scope for $
  2. Attach plugin to $.fn alias
  3. Add implicit iteration
  4. Enable chaining
  5. Add default options
  6. Add custom options
  7. global custom options
<div id="counter1">
</div>
<div id="counter2">
</div>
<script>
(function($) {
    $.fn.count = function(customOptions){

        var options = $.extend({},$.fn.count.defaultOptions, customOptions);
       
        return this.each(function(){
            var $this = $(this);
            $this.text(options.startCount);
            var myInterval = window.setInterval(function(){
                var currentCount = parseFloat($this.text());
                var newCount = currentCount+1;
                $this.text(newCount+'');
            }, 1000);
        });
       
    };
       
    $.fn.count.defaultOptions = {
        startCount:'100'
    };

})(jQuery);
 
jQuery.fn.count.defaultOptions.startCount = '300';

jQuery('#counter1').count();
jQuery('#counter2').count({startCount:'500'});
 
</script>