function adjustHeight(textarea, event){
    var sHeight = textarea.scrollHeight;
    var cHeight = textarea.clientHeight;
    var ekey = event.keyCode;
    var dif = sHeight - cHeight;
    if (dif){
        if (isNaN(parseInt(textarea.style.height))){
            textarea.style.height = textarea.scrollHeight + "px"
        }else{
            textarea.style.height = parseInt(textarea.style.height) + dif + "px"
        }
    }
}

$(textarea).keydown(function(event){adjustHeight(textarea, event);});

$(textarea).on('change keyup paste',function(event){adjustHeight(textarea, event);});