listbox

[bet]

Hola Nancy, probá con este código a ver si te sirve:

<pre>
&lt;html&gt;
&lt;head&gt;
&lt;title&gt; New Document &lt;/title&gt;
&lt;script language=&quot;JavaScript&quot;&gt;
&lt;!--
function validarSel(){
if (form.tipo.value==&quot;null&quot;){
alert (&quot;Por favor, indique el tipo que es.&quot;);
return (false);

}
}
//--&gt;
&lt;/script&gt;
&lt;/head&gt;

&lt;body&gt;

&lt;form method=post action=&quot;&quot; name=&quot;form&quot;&gt;
&lt;select name=&quot;tipo&quot; onChange=&quot;validarSel();&quot;&gt;
&lt;option value=&quot;null&quot;&gt;--seleccione--&lt;/option&gt;
&lt;option value=&quot;docente&quot;&gt;Profesor&lt;/option&gt;
&lt;option value=&quot;administrativo&quot;&gt;Empleado&lt;/option&gt;
&lt;/select&gt;

&lt;/form&gt;
&lt;/body&gt;
&lt;/html&gt;
</pre>

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