请求blob类型时显示响应错误文本

I have made a XMLHttpRequest with the 'responseType' set to 'blob' to a php script, is it possible i return more than one type of response? If script can run successfully, response with 'contentType/application/zip' but if the script failed, response with 'string'(error text). I try to response a string in my php script but, in my javascript, i set the XHR.responseType = 'blob'.

In PHP

if(someThingWrong)
{
echo "Archive not found"; //Repsonse is DOMString
header("HTTP/1.1 404 Not Found"); 
exit;
}
else
{
header("Content-type: application/zip"); //Response is octe-Stream or zip
header("Content-Disposition:  attachment; filename=\"" . basename($newZipFile) . "\"" );
readfile($newZipFile);  
}

In Javascript

XHR.open("POST", "anycode.php");
XHR.responseType = "blob";

When i try to access the xhr.ResponseText, it show 'undefined'.

    if(XHR.status == 404) 
    {alert(XHR.ResponseText);}

Any help is greatly appreciated.

You can use a FileReader object to get the response as text.

if(XHR.status == 404){ 
    var fr = new FileReader();
    fr.onload = function(e){
        alert(e.target.result);
    }
    fr.readAsText(XHR.response);
}