var request = null;
try{
    request = new XMLHttpRequest();
}catch (trymicrosoft){
    try{
        request = new ActiveXObject("Msxml2.XMLHTTP");
    }catch (othermicrosoft){
		try{
			request = new ActiveXObject("Microsoft.XMLHTTP");
		}catch (failed){
			request = null;
		}
	}
}
if (request == null){
	alert("Erro ao criar requisição de objeto!");
}