New Session ID when Using Isomorphic Fetch - node.js

Question

I have an unexpected behavior when using isomorphic-fetch vs. request-promise related to Express sessions (and Express session ID in particular):
As part of the troubleshooting process, I implemented two methods in client.js for calling endpoints in server.js: 1) isomorphic-fetch, and 2) request-promise.
Client.js
// Method 1: isomorphic-fetch
require('es6-promise').polyfill();
require('isomorphic-fetch');
fetch('http://localhost:3000', {
credentials: 'same-origin',
})
.then(function(response) {
console.log(response.status);
});
fetch('http://localhost:3000', {
credentials: 'same-origin',
})
.then(function(response) {
console.log(response.status);
});
// Method 2: request-promise
var rp = require('request-promise').defaults({
jar: true
});
function requestPage() {
return rp('http://localhost:3000/');
}
requestPage()
.then(console.dir)
.then(requestPage)
.then(console.dir)
.catch(console.error);
Server.js
var app = require('express')();
app.use(require('morgan')('dev'));
var session = require('express-session');
var FileStore = require('session-file-store')(session);
app.use(session({
name: 'server-session-cookie-id',
secret: 'my express secret',
saveUninitialized: true,
resave: true,
store: new FileStore(),
cookie: {
secure: false
}
}));
app.get('/', function initViewsCount(req, res, next) {
console.log('req.session.id = ' + req.session.id);
if (typeof req.session.views === 'undefined') {
req.session.views = 1;
return res.end('Welcome to the file session demo. Refresh page!');
}
return next();
});
app.get('/', function incrementViewsCount(req, res, next) {
console.assert(typeof req.session.views === 'number',
'missing views count in the session', req.session);
req.session.views++;
return next();
})
app.use(function printSession(req, res, next) {
console.log('req.session', req.session);
return next();
});
app.get('/', function sendPageWithCounter(req, res) {
res.setHeader('Content-Type', 'text/html');
res.write('<p>views: ' + req.session.views + '</p>\n');
res.end();
});
var server = app.listen(3000, function () {
var host = server.address().address;
var port = server.address().port;
console.log('Example app listening at http://%s:%s', host, port);
});
When I execute node client.js, here is the output of the server:
req.session.id = deWKCvqcyGiAvVSUvHv2Db7sjvE7xN1E
req.session.id = MxLHWjbMMvV4GRfPSf6sQ12XvauiJJot
req.session.id = A3KTLMdBopQ7pAfcTsJhnzzdokdA7hGI
GET / 200 1.407 ms - -
GET / 200 7.625 ms - -
GET / 200 0.728 ms - -
req.session.id = A3KTLMdBopQ7pAfcTsJhnzzdokdA7hGI
req.session Session {
cookie:
{ path: '/',
_expires: null,
originalMaxAge: null,
httpOnly: true,
secure: false },
views: 2,
__lastAccess: 1517449125197 }
GET / 200 6.902 ms - -
I confirmed that method 2 (request-promise) successfully persists the session on the server. In other words, session A3KTLMdBopQ7pAfcTsJhnzzdokdA7hGI is associated with this method.
However, as observed from the output, method 1 (isomorphic-fetch) generates two separate sessions on the server.
Question: Why does isomorphic-fetch create two separate sessions on the server?
Troubleshooting performed:
I replaced localhost with 127.0.0.1, but this did not change the behavior.
I replaced same-origin with include, but this did not change the behavior.
Environment:
node v6.10.3
isomorphic-fetch 2.2.1
request-promise 4.2.2