JavaScript creating ZIP file from existing folder

Question

Using JSZip, I need to get all items in an already existing folder. so I do a loop over a folder and add all items to the zip object.

Once I have my zip element complete, I start creating my zip file. But it creates an empty zip file without all my .json and .txt files.

I do not know why, the function addFolderToZip returns all the files and also in debug mode I can see the objects in the zip.

What is wrong with my code, please can someone help?

Here my functions: backupBasePath is normal absolute path

import JSZip from 'jszip';

async function createZip() {
    const zip = new JSZip();

    // Add the contents of the folder to the zip
    await addFolderToZip(zip, backupBasePath, '');
    //zip.file("hello.txt", "Hello World\n");
    // Generate the zip file
    zip
        .generateNodeStream({type: 'nodebuffer', streamFiles: true})
        .pipe(fs.createWriteStream('Test1234.zip'))
        .on('finish', function () {
            console.log("Test1234.zip written.");
        })
}

async function addFolderToZip(zip, folderPath, relativePath) {
    const files = fs.readdirSync(folderPath);

    for (const file of files) {
        const filePath = `${folderPath}/${file}`;
        const relativeFilePath = `${relativePath}/${file}`;

        if (fs.statSync(filePath).isDirectory()) {
            // If it's a directory, create a subfolder in the zip
            zip.folder(relativeFilePath);
            // Recursively add the contents of the subdirectory
            await addFolderToZip(zip, filePath, relativeFilePath);
        } else {
            // If it's a file, add it to the zip
            zip.file(relativeFilePath, fs.readFileSync(filePath));
        }
    }
}

If I create a zip object using zip.file("hello.txt", "Hello World\n"); it works.>

I know there are some similar questions, but I do not get it.

best regards Manu