jszipdownload.html

<html>
<head>
<script src="jszip/dist/jszip.js"></script>
<script src="jszip/vendor/FileSaver.js"></script>

<script>

var fileURLs = ['https://raw.githubusercontent.com/FortuneStreetModding/fortunestreetmodding.github.io/main/_maps/Abwarten/Abwarten.yaml', 'https://raw.githubusercontent.com/FortuneStreetModding/fortunestreetmodding.github.io/main/_maps/Abwarten/Abwarten0.frb'];
var zip = new JSZip();
var count = 0;

downloadFile(fileURLs[count], onDownloadComplete);

function downloadFile(url, onSuccess) {
    var xhr = new XMLHttpRequest();
    xhr.onprogress = calculateAndUpdateProgress;
    xhr.open('GET', url, true);
    xhr.responseType = "blob";
    xhr.onreadystatechange = function () {
        if (xhr.readyState == 4) {
            if (onSuccess) onSuccess(xhr.response);
        }
    }
    xhr.send();
}

function onDownloadComplete(blobData){
    if (count < fileURLs.length) {
        blobToBase64(blobData, function(binaryData){
                // add downloaded file to zip:
                var fileName = fileURLs[count].substring(fileURLs[count].lastIndexOf('/')+1);
                zip.file(fileName, binaryData, {base64: true});
                if (count < fileURLs.length -1){
                    count++;
                    downloadFile(fileURLs[count], onDownloadComplete);
                }
                else {
                    // all files have been downloaded, create the zip
                    var promise = zip.generateAsync({type:"blob"});
                    promise.then(
                        function(blob) {
                            saveAs(blob, "hello.zip");
                        },
                    );

                }
            });
    }
}

function blobToBase64(blob, callback) {
    var reader = new FileReader();
    reader.onload = function() {
        var dataUrl = reader.result;
        var base64 = dataUrl.split(',')[1];
        callback(base64);
    };
    reader.readAsDataURL(blob);
}

function calculateAndUpdateProgress(evt) {
    if (evt.lengthComputable) {
        // ...
    }
}

</script>
</head>
<body>
<script>

</script>
</body>
</html>