This is what other forums have to say on this topic How does JavaScript interfere with Tor browser anonymity? - Tor Stack Exchange
javascript - What happens if I enable scripts globally in Tor browser? - Tor Stack Exchange
Why disable JavaScript in Tor? - Information Security Stack Exchange anonymity - Use of javascript in Tor browser - Tor Stack Exchange Can JavaScript break anonimity provided by Tor? - Information Security Stack Exchange
From the above link tried https://amiunique.org/ with settings set to safer, which has JS enabled only for https websites and the result is Yes! You are unique among the 2262620 fingerprints in our entire dataset Selected the safest option which disables javascript for all websites and the result is Javascript is disabled on your browser! Some of features may not work properly. but at the same time it said Yes! You are unique among the 2262620 fingerprints in our entire dataset. We created a new identity for this and no setting of the noscript extension was changed for either of the results. What does this mean? This is the settings page of Tor- http://dsbqrprgkqqifztta6h3w7i2htjhnq7d3qkh3c7gvc35e66rrcv66did.onion/security-settings/index.html
On reddit members have explained about this topic very well and even some users have also said how it can be used against a user https://www.reddit.com/r/TOR/comments/om5aiv/what_exactly_is_the_risk_of_running_javascript/
Now the question is that if tor or tor in tails is used and the safest setting in tor is selected, which means no javascript for all websites, then most of the websites dont work. Some wouldnt show anything, some wouldn’t let you register, some wouldn’t let you upload or attach a file and so on. What countermeasures does tor or tails has against this? Is one at the mercy of the websites that they wouldn’t track a user using javascripts?