jquery统计输入文字的个数并对其进行判断

<script type="text/javascript">
$(function() {

function albumName() {
var text = $("#album_name").val();
var counter = text.length;
$("#numtj var").text(counter);
$(document).keyup(function() {
var text = $("#album_name").val();
var counter = text.length;
$("#name_word").text(counter);
});
}
});
</script>

<input type="text" maxlength="30" class="int_txt" name="album_name" id="album_name">
<span class="count_txt"><span id="name_word">0</span>/30</span>