knockout.js - setting tab index for children in knockout binding -

i have table data bound using knockout. here, have parent-child rows. e.g.

 <tr>                                 <td>                                     <select data-bind="value:required, enable:requiredactive, attr:{tabindex: 43 * ($index() + 1) }">                                         <option value="e">eligible</option>                                         <option value="o">on</option>                                         <option value="f">off</option>                                     </select>                                 </td>                                 <td>                                    <input data-bind="value:setuptime, attr: { title: tabindex: 44 * ($index() + 1) }"/>                                    <input data-bind="value:closetime, attr: { title: tabindex: 45 * ($index() + 1) }" />                                 </td>                                 <td>                                     <table>                                         <tbody data-bind="foreach: worksegments">                                             <tr>                                                 <td>                                                     <select data-bind="options:locations, value:location, optionstext: 'name', optionsvalue: 'id', attr:{tabindex: 49 * ($parentcontext.$index + 1) }" >                                                     </select>                                                 </td>                                             </tr>                                         </tbody>                                     </table>                                 </td>                                 <td>                                     <table>                                         <tbody data-bind="foreach: worksegments">                                             <tr>                                                 <td>                                                     <select class="combobox" data-bind="options:employeeroles, value:role, optionstext: 'name', optionsvalue: 'id', attr:{tabindex: 49 * ($parentcontext.$index + 1)}" >                                                     </select>                                                 </td>                                             </tr>                                         </tbody>                                     </table>                                 </td>                              </tr> 

here, location , employeerole drop downs children , can occur multiple times within parent. therefore when setting tab index i've used '$parentcontext.$index', @ runtime, child controls tabindex='nan'

i've tried $parent.index(), no luck.

appreciate help

you should use $parentcontext.$index() not $parent.index():

<select data-bind="options:locations, value:location, optionstext: 'name', optionsvalue: 'id', attr:{tabindex: 49 * ($parentcontext.$index() + 1) }" >                                                     </select> 

here working example: http://jsfiddle.net/cvl4q/