server.js

var express = require("express");
var app = express();
var bodyParser = require("body-parser");
var mongoose = require("mongoose");
var Details = require("./app/models/details");
var MongoClient = require("mongodb").MongoClient;

// Configure app for bodyParser()
// lets us grab data from the body of POST
app.use(
  bodyParser.urlencoded({
    extended: true
  })
);
app.use(bodyParser.json());

// Set up port for server to listen on
var port = process.env.PORT || 3001;

// Connect to DB
var url = "mongodb://adhi:password123@ds141796.mlab.com:41796/signup";
MongoClient.connect(url, (err, db) => {
  const dbo = db.db("signup");

  //API Routes
  var router = express.Router();

  // Routes will all be prefixed with /API
  app.use("/api", router);

  //MIDDLE WARE-
  router.use(function (req, res, next) {
    console.log("FYI...There is some processing currently going down");
    next();
  });

  // test route
  router.get("/", function (req, res) {
    res.json({
      message: "Welcome !"
    });
  });

  router.route("/details-update").post(function (req, res) {
    var exits = {
      pno: req.body.pno

    };
    var updatevalue = {
      pno: req.body.pno,
      bname: req.body.bname,
      email: req.body.email,
      baddress: req.body.baddress,
      btype: req.body.btype,
      fyear: req.body.fyear,
      booksdate: req.body.booksdate
    };
    console.log(exits);
    console.log(updatevalue);
    dbo
      .collection("details")
      .updateMany(exits, updatevalue, function (err, res) {
        if (err) throw err;
        console.log("1 document updated");
        db.close();
      });
  });

  router
    .route("/details")
    .post(function (req, res) {
      let status = true;
      var person = new Details();
      person.bname = req.body.bname;
      person.pno = req.body.pno;
      person.email = req.body.email;
      person.baddress = req.body.baddress;
      person.btype = req.body.btype;
      person.fyear = req.body.fyear;
      person.booksdate = req.body.booksdate;

      dbo
        .collection("details")
        .find({})
        .toArray(function (err, result) {
          if (err) throw err;
          for (var i = 0; i < result.length; i++) {
            if (person.pno == result[i].pno) {
              status = false;
              console.log(status);
            }
          }
          console.log(status);
          if (status == true) {
            dbo.collection("details").insertOne(person, function (err, res) {
              if (err)
                throw {
                  message: "Error comes " + err.message
                };
              console.log("1 document inserted sucessfully");
              // res.send do not work here
            });
          }
          res.send("Proccess successfully done...");
          return status;
        });
    })
    .get(function (req, res) {
      dbo
        .collection("details")
        .find({})
        .toArray(function (err, result) {
          if (err) throw err;
          console.log(result);
          db.close();
        });
      res.send("done");
    });
});
// Fire up server
app.listen(port);

// print friendly message to console
console.log("Server listening on port " + port);