获取下拉列表框的值是数组，split，$.inArray示例

var product_id = $(this).val()

console.log(product_id);
if(product_id == '51'){alert(111);}
if(product_id[0] == '51'){alert(222);}

var result = $.inArray(product_id,arr_product_ids);

var result = $.inArray(product_id[0],arr_product_ids);