Germain's User Replay feature showing what a User did while browsing a web application built in MarkoJS/NodeJS.
And other examples:
In addition, this User Session Replay feature allows you to monitor and watch any users on any web application (built in any flavor of HTML/JS), as if you were watching each User's browser behind their shoulders. User Replays/Videos are a complete reconstruct/recording of the User's browser, and mouse moves, clicks, typing. User Session Replay is GDPR compliant (i.e. sensitive data can be excluded, encrypted, anonymized, etc)