input累加赋值

<tr>
<td rowspan="2" class="D_td_t_l"><span class="red">*</span><span>企业填报数据包含海关代码有：</span></td>
<td class="no_border"><input id="hgdm" type="text" class="D_text_a" /></td>
<td class="D_td_b no_border"><input id="hgdm_plus" type="button" class="search_plus" /></td>
<td class="D_td_b no_border"></td>
<td class="D_td_b no_border"></td>
</tr>
<tr>
<td colspan="2"><input id="hgdm_val" type="text" class="D_text_b" /></td>
<td class="D_td_b"><input id="hgdm_m" type="button" class="search_m" /></td>
<td class="D_td_b"></td>
</tr>

//企业填报数据包含海关代码有 赋值
$("#hgdm_plus").on("click", function () {
var hgdm = $("#hgdm");
var hgdm_val = $("#hgdm_val");
if (hgdm.val() != "") {
if (hgdm_val.val() == "") {
hgdm_val.val(function (i, v) {
return v + hgdm.val();
});
hgdm.val("");
} else {
hgdm_val.val(function (i, v) {
return v + "," + hgdm.val();
});
hgdm.val("");
}
}
});

$("#hgdm_m").on("click", function () {
$("#hgdm_val").val("");
});