Uploading multiple and Single files using Node.js and Express.js with MongoDB.

const upload_PAN = multer({
        storage: multer.diskStorage({
            destination: function (req, file, cb) {
                cb(null, "uploads_tender")
            },
            filename: function (req, file, cb) {
                let name = file.originalname;
                cb(null, file.fieldname + "_" + Date.now() + ".pdf")
            }
        })
    }).any('PAN_file', 'EMD_file', 'Aadhar_file')

const upload_PAN = multer({
        storage: multer.diskStorage({
            destination: function (req, file, cb) {
                cb(null, "uploads_tender")
            },
            filename: function (req, file, cb) {
                let name = file.originalname;
                cb(null, file.fieldname + "_" + Date.now() + ".pdf")
            }
        })
    }).single('Aadhar_file')

  app.post("/upload_tender_file", upload_PAN, (req, res) => {
        let k = req.body;
        let f = req.files;
        let temp = req.files.length;
        let edm=f[0];
        let pan=f[1];
        let aadhar=f[2]

        console.log(temp);
        console.log(k);

        let size = 1;
        if (req.session && req.session.userid) {
            res.json({
                status: "warn",
                message: "Session already exists !",
                isLogged: true,
                lastUpdated: req.session.lastUpdated,
                isLatest: false,
                profile: req.session.profile,
            });
        }
        // check if any value is not null
        else if (size != 0
            && edm
            && pan
            && aadhar
            && k.tenderName
            && k.email
            && k.tenderValue
            && k.amountWords
            && k.endDate) {
            // check if record already exists...
            db.collection("tender_files").findOne(
                { projection: { _id: 1, email: 1, tenderName: 1 } },
                (error, result) => {
                    if (result && result._id) {
                        res.json({
                            status: "error",
                            message: "File already exists !",
                            isLogged: false,
                        });
                    }
                    // tenserName doesn't exists, create one
                    else {
                        let obj = {
                            tenderName: k.tenderName,
                            email: k.email,
                            profile: {
                                tenderName: k.tenderName,
                                email: k.email,
                                endDate: k.endDate,
                                amountWords: k.amountWords,
                                edm: edm,
                                pan:pan,
                                aadhar:aadhar,
                                tenderValue: k.tenderValue,
                            },
                        };
                        db.collection("tender_files").insertOne(obj, (error, results) => {
                            if (error) {
                                res.json({
                                    status: "error",
                                    message: error,
                                    isLogged: false,
                                });
                                throw error;
                            }
                            // Records inserted, auto log in
                            else {
                                // log it in
                                res.json({
                                    status: "success",
                                    message: "File Uploaded !",
                                    isLatest: true,
                                    isLogged: true,
                                    profile: obj.profile,
                                });
                            }
                        });
                    }
                }
            );
        } else {
            res.json({
                status: "error",
                message: "Empty or invalid data",
                isLogged: false,
            });
        }
    });