counter limit textarea

gistfile1.js

 // limitador de caracteres
   var limitText = function() {
     var count = 600; // value limit caracter
     var txt = document.forms[0].text.value;
     var len = txt.length;
     var countText = document.getElementById("your-counter"); // create element your html
     if(len > count){
             txt = txt.substring(0,count);
             document.forms[0].text.value = txt;
             return false;
     }
     countText.innerHTML = count-len;
   }
   // use jquery or other
   $("textarea").keyup(function(){
      limitText();
   })
})