var request = false;   
try  
{// ��������IJ�ͬ����XMLHttpRequest����   
    request = new XMLHttpRequest ();   
} catch ( trymicrosoft )   
{   

    try  
    {   
        request = new ActiveXObject ( "Msxml2.XMLHTTP" );   
    } catch ( othermicrosoft )   
    {   
        try  
        {   
            request = new ActiveXObject ( "Microsoft.XMLHTTP" );   
        } catch ( failed )   
        {   
            request = false;   
        }   
    }   
}   
  
if ( ! request ) alert ( "Error initializing XMLHttpRequest!" );