JQuery .on('keydown',...) not triggering on new elements

Question

I looked through some related questions, but none helped me figure out my problem.

I have my own dynamic data grid form built from scratch, where rows of data and field columns can be added/removed etc. I'm trying to improve the usability so that pressing the enter key will create a new field column and give focus to it. Here's the code that does this so far:

$('#data_fields').on('keydown','._field',function(e){
    if(e.which==13)
    {
        $('#addfield').click();
        var o=$(this).parent().parent();
        var l=$(o).children().length-2;
        var f=$(o).find("td:eq("+l+")").find("._field");
        $(f).focus();
    }
});

#addfield is a button which adds the field column when clicked.

._field is an input box where the name of the field is written.

#data_fields is a tr containing cells with ._field input boxes in them.

However, the ._field input boxes in the new columns do not have the special superelement keydown ability. Whats more, if I change the ('#data_fields') selector for .on() to (document), it doesn't even give current elements the keydown callback.

Here's the HTML, sorry that its a bit messy but I use templates in PHP and stuff:

<thead id="doc_fields">
  <tr id="delrow">
  <tr id="data_fields">
    <td style="padding:2px"><input class="_field" type="text" onkeyup="sync_doc_table();" onchange="sync_doc_table();" style="width:90%" value="" name="Fields[]"></td>
    <td style="padding:2px"><input class="_field" type="text" onkeyup="sync_doc_table();" onchange="sync_doc_table();" style="width:90%" value="b" name="Fields[]"></td>
    <td style="padding:2px"><input type="text" style="width:90%" value="" name="Fields[]" onchange="sync_doc_table();"></td>
    <td style="padding:2px"><input type="text" style="width:90%" value="" name="Fields[]" onchange="sync_doc_table();"></td>
    <td id="addcol" class="midi" style="width:25px" rowspan="3">
      <a id="addfield" onclick="inscol('#addcol','<td style=\'padding:2px\'><input onchange=\'sync_doc_table();\' type=\'text\' name=\'Fields[]\' value=\'\' style=\'width:90%\' /></td>');addcol('#typerow','<td><select name=\'Type[]\' style=\'width:91%\'><option value=\'integer\'>integer</option><option value=\'double\'>double</option><option value=\'string\' selected=\'selected\'>string</option></select></td>');addcol('#delrow','<td class=\'center _delly\'><a href=\'#\' onclick=\'del_doc_field($(this).parent());return false;\'><img src=\'/images/icons/x.png\' alt=\'[Del]\' /></a></td>');$('._colsp').attr('colspan', $('#addrow').attr('colspan') + 1);$('<td><input type=\'text\' name=\'Data[][]\' value=\'\' style=\'width:90%\' /></td>').insertBefore('.datarow ._delly');return false;" href="#">
    </td>
  </tr>
  <tr id="typerow">
</thead>

Answer 1

From What I can tell it's because your input class that's being appended doesn't have a _field class in it.