Regular Expressions 101

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/
\,(?=[^,]*$)
/
g
\, matches the character , with index 4410 (2C16 or 548) literally (case sensitive)
Positive Lookahead
(?=[^,]*$)
Assert that the Regex below matches
Match a single character not present in the list below
[^,]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
, matches the character , with index 4410 (2C16 or 548) literally (case sensitive)
$ asserts position at the end of the string
Global pattern flags
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.

Regular Expression
No Match

/
/
g

Test String