2중 셀렉트 질문드립니다.

select name="product" id="product" class="cis"><option value="">선택하세요</option><option value="0001">가</option><option value="0002">나</option><option value="0003">다</option></select> <select name="model" id="model" class="cis"><option value="">선택하세요</option></select><script type="text/javascript" language="javascript">var model_value=new Array();model_value[가]='a,b,c';model_value[나]='e,f,g';$(function() {$("#product").bind("change", function() {var model=$(this).val();chang_model(model);});​});function chang_model(model){var model_id=document.getElementById("model");model_id.options.length = 1;model_id.options[0].selected = true;model_id.options[0].text  = "선택하세요";model_id.options[0].selected = true;​num=model_value[model].split(",");num_l=num.length;model_id.option.length=num_l+1;for(i=0;i<num_l;i++){model_id.option[i+1].value=num[i];model_id.option[i+1].text=num[i];}}</script>