how can i put onchange in
$regionslistx[]= JHTML::_('select.option', "0", JText::_( '--No Location--' ),'value','text' );
or
$lists['regionslist' ]= JHTML::_('select.genericlist', $regionslistx, 'City', '', 'value', 'text', $lx );
In the second case, where you have the empty argument, place the function you would like to use:
$lists['regionslist' ]= JHTML::_('select.genericlist', $regionslistx, 'City', 'onchange=\"YOURFUNCTION()\"', 'value', 'text', $lx );
Also check the documentation: http://api.joomla.org/Joomla-Framework/HTML/JHTMLSelect.html
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