check magic number before upload

index.js

var express = require("express")
var multer = require('multer')
var app = express()
var path = require('path')
var fs = require('fs')

var ejs = require('ejs')
app.set('view engine', 'ejs')

var MAGIC_NUMBERS = {
	jpg: 'ffd8ffe0',
	jpg1: 'ffd8ffe1',
	png: '89504e47',
	gif: '47494638'
}

function checkMagicNumbers(magic) {
	if (magic == MAGIC_NUMBERS.jpg || magic == MAGIC_NUMBERS.jpg1 || magic == MAGIC_NUMBERS.png || magic == MAGIC_NUMBERS.gif) return true
}

app.get('/api/file', function(req, res) {
	res.render('index')
})

var upload = multer({
	storage: multer.memoryStorage()
}).single('userFile')

app.post('/api/file', function(req, res) {
	upload(req, res, function(err) {
		var buffer = req.file.buffer
		var magic = buffer.toString('hex', 0, 4)
		if (checkMagicNumbers(magic)) {
			var wstream = fs.createWriteStream('./uploads/' + req.file.fieldname + '-' + Date.now() + path.extname(req.file.originalname))
			wstream.write(buffer)
			res.end('File is uploaded')
		} else {
			res.end('File is no valid')
		}
	})
})

var port = process.env.PORT || 8080
app.listen(port, function() {
	console.log('Node.js listening on port ' + port)
})

You should think about JPEG RAW. According to Wiki magic number for it is ff d8 ff db