Revisa este ejemplo:
Código PHP:
<html>
<head>
<script language="JavaScript">
var muestraTexto = false;
function cambiaSelector(){
with (window.pantalla.document){
muestraTexto = (frm.selector.selectedIndex == 1? true: false);
}
formulario();
}
function formulario(){
with (window.pantalla.document){
open();
writeln("<html>\n<body>");
writeln("<form name='frm'>");
writeln("<select name='selector' onchange='parent.cambiaSelector()'>");
writeln(" <option" + (muestraTexto? "": " selected") + ">Combo solo</option>");
writeln(" <option" + (muestraTexto? " selected": "") + ">Combo y texto</option>");
writeln("</select>");
writeln("<br>");
if (muestraTexto){
writeln("<input type='text' name='campoTexto' value='algo'>");
}
writeln("</form>");
writeln("</body>\n</html>");
close();
}
}
document.writeln("<frameset rows='100%,*' onload='javascript:parent.formulario()'>");
document.writeln(" <frame name='pantalla' src='DummyPage.htm'>");
document.writeln(" <frame src=''>");
document.writeln("</frameset>");
</script>
</head>
</html>