Error uploading files using Multer in NodeJs

I am currently working on nodeJS to code APIs. I dont have much experience on coding, apologies if this might be a silly question. I tried to write a API for uploading files that can be named and its directory path is set dynamically. I could partially achieve objectives but facing little problems. I will show my code.

    var express =   require("express");
    var multer  =   require('multer');
    var app         =   express();
    var crypto=require("crypto")
    var mime=require("mime");
    var path='./uploads'
    var fs = require('fs');
var mkdirp = require('mkdirp');



var storage =   multer.diskStorage({
  destination: function (req, file, callback) {
    callback(null, path);
    console.log("Im in storage destination"+path);
  },
  filename: function (req, file, callback) {
    console.log("Im in storage filename"+path);
    //callback(null, file.fieldname + '-' + Date.now());



    crypto.pseudoRandomBytes(16, function (err, raw) {
      callback(null, Date.now() + '.' + mime.extension(file.mimetype));
    });
  }
});

    var upload = multer({ storage : storage}).single('userPhoto');

app.post('/photo',function(req,res){
    path += "/pics/shanmu/";

    console.log("Im in post , outside upload"+path);
    upload(req,res,function(err) {
        console.log("Im in post , inside upload"+path);
        if(err) {
            return res.end("Error uploading file.");
        }
        res.end("File is uploaded"+path);
        console.log("File is uploaded"+path);
    });
});

app.listen(3000,function(){
    console.log("Working on port 3000");
});

And this is my Folder structureWhen I run my code the file should get uploaded in uploads folder which you can see in the image and also has another folder inside and another (./uploads/pics/shanmu) when i try to trigger it form the postman I can do it only once, when i tries again i couldnt upload my files. Please help. Thanks in advance.

via shanmu sanjay