In 2013 gov.uk did a test to see how many people received ran their site's javascript[1].
They found that for 1.1% of visitors the javascript didn't run.
0.9% was because of errors — network errors, browser-extensions breaking the code, a mobile user going through a tunnel.
0.2% was people who actively blocked javascript.
I'm writing an small article about making sure websites work for that 0.2%.
1. https://gds.blog.gov.uk/2013/10/21/how-many-people-are-missing-out-on-javascript-enhancement/