[Middleware: cookie-session] How is 'req.session' change detected in this package?

From the Readme.md file,The middleware will automatically add a Set-Cookie header to the response if the contents of req.session were altered.Where is the implementation of detecting req.session change? Can somebody point me to the code or explain me how is this achieved?

Submitted January 25, 2020 at 08:12PM by zyx422