Filter files on the basis of extension using Multer in Express JS

An example using multer:

var storage = multer.diskStorage({ //multers disk storage settings    destination: function (req, file, cb) {        cb(null, './public/uploads/')    },    filename: function (req, file, cb) {        var datetimestamp = Date.now();        cb(null, file.fieldname + '-' + datetimestamp + '.' + file.originalname.split('.')[file.originalname.split('.').length -1])    }});var upload = multer({ //multer settings    storage: storage,    fileFilter: function (req, file, callback) {        var ext = path.extname(file.originalname);        if(ext !== '.png' && ext !== '.jpg' && ext !== '.gif' && ext !== '.jpeg') {            return callback(new Error('Only images are allowed'))        }        callback(null, true)    },    limits:{        fileSize: 1024 * 1024    }}).single('profilepic');

Excerpted from Node.js - File upload. The original authors were Iceman and Mikhail. Attribution details can be found on the contributor page. The source is licenced under CC BY-SA 3.0 and may be found in the Documentation archive. Reference topic ID: 4080 and example ID: 14210.

This is very helpful thank you. In my case I needed to add a middleware to ensure a JWToken was in place and build it with XHR. If someone else is needing help with this here is what worked for me. It can be easily accomplished when passing the token in the XHR header.

Client:

    const loadHandler = event =>{        // loadHandler mandate    }    const errorHandler = event => {        // error mandate    }    const abortHandler = event => {        // abort mandate    }    const data = new FormData()    data.append('file', upFile)    var formData = new FormData();    var xhr = new window.XMLHttpRequest();    formData.append('files', upFile); // this is a state object set onChange    xhr.open('post', '/uploadFile', true);    xhr.setRequestHeader('token', thetoken); // Passing token in header    xhr.addEventListener("load", loadHandler, false);    xhr.addEventListener("error", errorHandler, false);    xhr.addEventListener("abort", abortHandler, false);    xhr.send(formData);

Server

const express = require('express'),      app= express.Router(),      rf = require('./RoutFuctions');...app.post('/uploadFile', rf.verifyToken, function (req, res, next) {     // upload portion above});

RoutFunctions.js

const jwt = require('jsonwebtoken')const tokenTest = (token, res, jwt, caller, next) => {    jwt.verify(token, process.env.SECRET_KEY, err => {        if(err) {          res.sendStatus(403);          console.log('could not verify token');        } else {          console.log("token verified");          next(); // Next middleware        }    });}exports.verifyToken = function(req, res, next) {    if(req.body.token !== undefined) { // non upload scenario        var caller = ''        if(req.body.caller !== undefined) caller = req.body.caller;        tokenTest(req.body.token, res, jwt, caller, next)    } else {  // attempt to extract token in XHR header upload scenario      if(req.headers.token !== undefined){          var token = req.headers.token          tokenTest(req.headers.token, res, jwt, caller, next)      } else {          res.sendStatus(403);      }    }}

Complete Implementation for multiple or single files.

Note: for single file use .single('filename') or .array('filename',1)

  const express = require("express");  const app = express();  var session = require('express-session')  const multer = require("multer");  const path = require("path");  var storage = multer.diskStorage({ //multers disk storage settings    destination: function (req, file, cb) {        cb(null, path.join(__dirname,"uploads"))    },    filename: function (req, file, cb) {        var datetimestamp = Date.now();        cb(null, file.fieldname + '-' + datetimestamp + '.' + file.originalname.split('.')[file.originalname.split('.').length -1])    }  });  var upload = multer({ //multer settings    storage: storage,    fileFilter: function (req, file, callback) {        var ext = path.extname(file.originalname);        if(ext !== '.png' && ext !== '.jpg' && ext !== '.gif' && ext !== '.jpeg') {            return callback(new Error('Only images are allowed'))        }        callback(null, true)    },    limits:{        fileSize: 1024 * 1024    }  }).array('profile',2);  app.post("/upload", upload,(req, res) => {    res.json({      msg:"uploaded"    })  });  app.use((err,req,res,next)=>{    console.log(err.message);    res.status(404).json({      msg:err.message    })  })  app.listen(    8080,    (error) => {      if (error) {        console.log("error");      }    },    () => {      console.log("listening at port 8080");    }  );

Note: You can create your own custom error messages by extending Error and send custom messages and status in err,req,res,next block