cargando... en un combo dependiente

[esystemas]

holaalguien sabe como crear loadin,,,, 0 cargando..... antes que traga la data el cobo dependiente?

aqui lo que trate de hacer pero nose en que estoy fallando


function dd_change( n, max, prefix ){
if( n >= max-1 )
return; // the last dropdown, no need to query

//var prefix = 'dd_' ;
// reset all other dropdown options
var next = n+1;
for( var i = next; i < max; i ++ ){
var dd = document.getElementById(prefix +'_' + i );
if( dd && dd.length >= 1 ) dd.length = 1 ; // keep the first one '- select -'
};


// request drop down data from server
var me = this;
var http;
var isIE = navigator.appName == "Microsoft Internet Explorer";
if(isIE){
me.http = new ActiveXObject("Microsoft.XMLHTTP");
}else{
me.http = new XMLHttpRequest();
};


// build query string
var lookup = [];
for( var i = 0; i < next; i ++ ){
var v = document.getElementById(prefix +'_' + i ).value ;
lookup.push( "lookup[" + i + "]=" + escape( isIE ? Utf8.encode(v) : v ) );
};
lookup = lookup.join('&');

var url = '<?php echo PHPFMG_ADMIN_URL . '?mod=dd&func=lookup&' ; ?>n='+next+ '&field_name=' + prefix + '&' + lookup;
me.http.open('get', url);
me.http.onreadystatechange = function(){

if( me.http.readyState == 4 ){
// rebuild the next dropdown options
var eNext = document.getElementById(prefix +'_' + next );
if( !eNext )
return;

var data = me.http.responseText;
var opts = String(data).split("\n");
for( var j = 0, J = opts.length; j < J; j ++ ){
eNext.options[ eNext.length ] = new Option( opts[j], opts[j], false, false );
}; // for
}; //if

};
me.http.send(null);

}