function addLoadEvent(func) { 
    var oldonload = window.onload; 
    if (typeof window.onload != 'function') { 
        window.onload = func; 
    } else { 
        window.onload = function() { 
            oldonload(); 
            func(); 
        } 
    } 
} 
addLoadEvent(function() { 
    /* more code to run on page load */  
    setTimeout("preImg();", 4000 );
});