How to make dynamic dropdown with the help of javascript.

Hello, I am working on API, Its having code tags for dynamic content adding to the webpage. I want to take Theme categories names dynamically in dropdown menu with the tag <px:name />.
All the names i want to show in dropdown menu comes by the tag <px:name />. The result of this code it shows, seperate one by one. But i want it in dropdown only. Is it possible by loop. How can i do this?. Plz reply.



<px:category>
<px:themes>
<form>
<select>
<px:each>
<px:theme>

<option value=""><px:name /></option>
<px:start><input type="submit"/></px:start>

</px:theme>
</px:each>
</select>
</form>
</px:themes>
</px:category>