jquery循环获取每个表格的ID

<tr>
									<td height="20">
										<input
											type="hidden"
											class="row_id"
											value="${row[10]}"
										/>
									</td>
								</tr>

var value2;
			$(".row_id").each(function() {
						// $(".row_id").length
						value2 += $(this).val() + ",";
					});
			if ($.trim(value2)) {
				value2 = value2.replace("undefined", "");
				value2 = value2.substr(0, value2.length - 1);
			}
			alert(value2);