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,            });        }    });