problem with syntax updating hidden form field
I have a number of table rows in my table and each has a hidden form field which I'm trying to update using the syntax below. When I run it I get back undefined for the alert. Can anyone let me know what I'm doing wrong? The table row id is tw_cjid_10775_4. Thanks.
$("#tw_cjid_10775_4 > input[name^='hf_lineitemid_']").val(lineitemid);
alert($("##tw_cjid_10775_4 > input[name^='hf_lineitemid_']").val());