This is a content script that uses some builtin JS methods to calculate the dislikes on a YouTube video. It does so by extracting both the average rating and like count of the video and using a weighted average calculation to compute an estimate of the dislike count.
Thanks to ReturnYoutubeDislikes for inspiration on this method.
The extrapolation of this data is ineffcient but the calculation method provides a reasonable estimate for the dislike count.
This script uses an XMLHttpRequest to get the average rating, which is no longer provided within a YouTube video's source code.