In NextJS, I have am passing event.target.files into upload.js. To do this, I am using Axios:

const formData = new FormData()
for (let i = 0; i < formFiles.length; i++) {
    formData.append('files[]', formFiles[i])
}
const response = await axios.post("/api/upload", formData, {
    headers: {"content-type": "multipart/form-data"},
    onUploadProgress: (progressEvent) => {
        const percentage = (progressEvent.loaded * 100) / progressEvent.total;
        console.log(percentage)
        setProgress(+percentage.toFixed(2));
    },
})

In Upload.js, I pass the formdata like so:

const parseFormData = (request) => {
    return new Promise((resolve, reject) => {
        const form = new formidable.IncomingForm({
            multiples: true,
            keepExtensions: true,
        });
        form.parse(request, (err, fields, files) => {
            if (err) {
                console.log("Form error: " + err)
                reject(err);
            }
            resolve({ fields, files });
        });
    });
};

export default async function handler(request, response) {
    if (request.method === "POST") {
        const { files } = await parseFormData(request);
        const formFiles = files['files[]']
        console.log(formFiles)
        if(formFiles instanceOf Array) {
...

However if formFiles is a single file then it only passes the one file through, but it doesnt register as an array. If I pass multiple files through, then it works fine with formFiles instanceOf Array. But if there's only one file this fails. How can I accurately determine if theres one file, multiple, or none passed (Error~?)