When I get helper functions from stack overflow or similar, I normally add a comment with a link to the article, mostly for my own sake so if there's any problems later I can re-read the article to get more info, or use it to try and find other solutions.
I used to do that on complete copy and paste parts.
Now we aren't allowed to do so. If stackoverflow.com is used you have to adjust the answer so that in court your code will not be a copy. They are afraid of users licenseing their code afterward.
For JS shit I usually have to rewrite them because they aren't production quality in terms of readability. Still really useful for getting answers on obscure stuff
The quality is definitely varying, the hardest part is to find a example that fits what you expect, or looks like it can be refactored into what you need.