problems with XMLHttpRequest or is a server setting problem loading a gpx file

Question

I'm Italian almost a newbie in javascripting and server side rule configuration. I'm creating a webside page, and intend to use a part of code of gpxtruder.xyz.

I have permission of owner (Jim Denova jim@anoved.net) to use original code, as it's released under opensource license.

In index.html page code is following:

    <form enctype="multipart/form-data" method="get" name="gpxform">
            <p><input type="radio" name="gpxsource" value="0" id="gpxsource_upload" onchange="return toggle(event, 0, 'gpxfile') && toggle(event, 1, 'gpxsample');" />
                <label for="gpxsource_upload">Upload GPX:</label>
                <input type="file" id="gpxfile" /><br />
               <input type="radio" name="gpxsource" value="1" id="gpxsource_sample" onchange="return toggle(event, 0, 'gpxfile') && toggle(event, 1, 'gpxsample');" checked />
                 <label for="gpxsource_sample">Sample GPX:</label>
                <select id="gpxsample">
                    <option value="0" selected>South Mountain</option>
                    <option value="1">Vestal XX (20k road race)</option>
                </select>
                <h1>Hello, my name is <span id="name"></span></h1>
              <script>
                    let gpxsource = "1"
                let name = gpxsource;
                document.getElementById("name").innerHTML = name;
              </script>

you could choose a pre selected track to show result or load your own gpx file

parameters are sent to gpxtruder.js file, follows part of code processing data first part of code

    if (radioValue(form.gpxsource) === 0) {
    // Assign a local URL to the file selected for upload
    // https://developer.mozilla.org/en-US/docs/Web/API/URL.createObjectURL
    var files = document.getElementById('gpxfile').value;
                window.alert(gpxfile);
    //var files = document.getElementById('gpxfile').files;
                window.alert(files);
    if (files.length === 0) {
        Messages.error('No GPX file selected.');
        return;
    }
//  upload_url = window.URL.createObjectURL(files[0]);
        upload_url = files
} else {
    if (parseInt(form.gpxsample.value) === 0) {


        upload_url = "https://gpxtruder.xyz/gpx/SouthMtn.gpx";
    } else if (parseInt(form.gpxsample.value) === 1) {

        upload_url = "https://gpxtruder.xyz/gpx/VXX.gpx";
    } else {
        return;
    }
}
window.alert(upload_url);
window.alert(options);
loader(options, upload_url);

if (radioValue(form.gpxsource) === 0) {
    window.URL.revokeObjectURL(upload_url);
}

second part of code

var loader = function(options, gpx_url) {
window.alert(gpx_url);
Messages.clear();

var req = new XMLHttpRequest();
req.onreadystatechange = function() {
    if (req.readyState === 4 /*&& req.status == 200*/) {

        if (!req.responseXML) {
            Messages.error("This doesn't appear to be a GPX file.");
            return;
        }
window.alert(req.responseXML);
        // Attempt to parse response XML as a GPX file.
        var pts = Parser.file(req.responseXML, options.zoverride, options.zconstant);
        if (pts === null) {
            return;
        }

        // If all is well, proceed to extrude the GPX path.
        g = new Gpex(options, pts);
    }
};

// submit asynchronous request for the GPX file
req.open('GET', gpx_url, true);
req.overrideMimeType("text/xml");
req.send();

};

my problem is stricktly connected to upload_url = "https://gpxtruder.xyz/gpx/VXX.gpx"; if I change url address and insert my server web space, where I hosted gpx files,even if I use original file, page answer "This doesn't appear to be a GPX file."

I didn't find were problem could be.

Could be a javascript related problem? (but code and file are exacly a dupe of original) or could be a server side configuration problem were gpx file is hosted?

original file could be found

https://gpxtruder.xyz/index.html

https://gpxtruder.xyz/js/gpxtruder.js

thanks for help, if any possible.

Answer 1

Problem was a server side configuration, exactly a: CORS header 'Access-Control-Allow-Origin' missing

I'm a newbie and didn't know how browser console works and how could be useful

solved via .htaccess

   <IfModule mod_headers.c>
     Header set Access-Control-Allow-Origin "*"
   </IfModule>

answer found on CORS header 'Access-Control-Allow-Origin' missing