(function($){ 
     $.fn.extend({  
         limit: function(limit,element, classAlerta ) {
			
			var interval;
			var self = $(this);
					
			$(this).focus(function(){
				interval = window.setInterval(substring,100);
			});
			
			$(this).blur(function(){
				clearInterval(interval);
				substring();
			});
			
			function substring(){
				var val = $(self).val();
				var length = val.length;		
				if(typeof element != 'undefined')
					$(element).html((limit-length<=0)?'0':limit-length);
					
					if (limit-length < 10){
						$(element).addClass(classAlerta);
					}else{
						$(element).removeClass(classAlerta);
					}
					
				if(length > limit)
					$(self).val($(self).val().substring(0,limit));
			}
			
			substring();
			
        } 
    }); 
})(jQuery);