Because the file's name is just 'download' in your browser's eyes, you'll need to offer it extra information by using another HTTP header.
res.setHeader('Content-disposition', 'attachment; filename=dramaticpenguin.MOV');
You may also want to send a mime-type such as this:
res.setHeader('Content-type', 'video/quicktime');
If you want something more in-depth, here ya go.
var path = require('path');
var mime = require('mime');
var fs = require('fs');
app.get('/download', function(req, res){
var file = __dirname + '/upload-folder/dramaticpenguin.MOV';
var filename = path.basename(file);
var mimetype = mime.lookup(file);
res.setHeader('Content-disposition', 'attachment; filename=' + filename);
res.setHeader('Content-type', mimetype);
var filestream = fs.createReadStream(file);
filestream.pipe(res);
});
You may change the header value to anything you like. In this scenario, I'm checking the file's mime-type with a mime-type library called node-mime.
Another thing to keep in mind is that I've switched your code to utilise a readStream. Because node is designed to be asynchronous, employing any method with the word 'Sync' in the name is frowned upon.
To make things easier, Express includes a tool for this.
http://expressjs.com/en/api.html#res.download
app.get('/download', function(req, res){
const file = `${__dirname}/upload-folder/dramaticpenguin.MOV`;
res.download(file); // Set disposition and send it.
});