Thanks! Was it this one?
http://web.archive.org/web/20160304012151/http://tech.beatpo...
(no longer on the beatport site; tech.beatport doesn't seem to exist any more and the current beatport blog starts at 2015)
Yeah that's the one, I was looking at this post that uses Spotify and echonest too https://jmperezperez.com/bpm-detection-javascript/
I implemented and tested it and it worked quite well with electronic music.