Spotinfo.js is a fork of Naushikha's Spotify-Widget which is an open source spotify listening info widget made in html,css and js.
Spotinfo.js contains some changes like real time updating of the listening state and has an overall simplified structure and external css.
This Project underlies the AGPL-3.0 license.
You can find a live demo here.
The html and css part can be directly implanted into any website. The spotinfo.js file needs to be put somewhere into the websites folder structure and the worker.js is the code for the worker, which you can essentially just copy paste into your worker.
Further instructions can be found here