I am recieving files using node js on another computer and I want to send custom metadata from the computer I am uploading from. addonData is an {} object with key value pairs that have information about the files I’m uploading. I am using formData.append to add addonData, but on my server console.log(req.body) returns {} (req has tons of data including req.body: {},).

const app = express();
app.use(express.json());

...

async function uploadFile(filePath, uploadUrl, fileName, addonData) {

        ...

        formData.append('file', fileBuffer, fileName);
        formData.append('addonData', '[' + JSON.stringify(addonData) + ']');

        // Perform the fetch request to upload the file
        const response = await fetch(uploadUrl, {
            method: 'POST',
            body: formData, // Automatically sets 'Content-Type': 'multipart/form-data'
        });

        ...

}

Then on my computer recieving the uploads:

const app = express();
app.use(express.json());

...

POST route for handling file uploads
app.post('/upload', (req, res) => {

    const form = new formidable.IncomingForm({
        uploadDir: uploadDirectory,
        keepExtensions: true,
        keepFilenames: true,
        filename: function (name, ext, part) {
            // Use the original filename
            return part.originalFilename;
        }
    })

    form.parse(req, (err, fields, files) => {
        if (err) {
            console.error('Error processing upload:', err);
            return res.status(500).send('An error occurred during the upload.');
        }
        console.log(req.body) // returns {}
        addonDataStr = req.body.addonData; // undefined
        addonData = JSON.parse(addonDataStr); 
        // Update addonData
        addonData.new_filename = files.file[0].newFilename;
        addonData.path_server = files.file[0].filepath;
        addonData.size_bytes = files.file[0].size;
        addonData.IP = req.ip;
        addonData.req_headers = req.headers;
        
        appendFileNameKey();
        res.status(200).send('File uploaded successfully.');
    });
});

When I try to add headers: {'Content-Type': 'application/json'} to the first script the server gives the error “Unexpected token – in JSON at position 0”. The files are uploading correctly using the code above if I comment out trying to receive metadata (addonData). Thanks for the help.