javascript – RegExp returning group matches

I am trying to make a regular expression to match quantities from a string using javascript

for example if I have "3-Ply Tissue, 23" x 24", 50/bg", I want to extract "50/bg". There can be multiple matches per string. Another stipulation is that the units on the bottom of the fraction can come from a list, for simplicity lets say I have "bg" and "cs".

My regex is /\d+\/(bg|cs)/gi

When I execute the regular expression, this is what it returns.

> reg.exec(myString)
[
  '50/bg',
  'bg',
  index: 25,
  input: '3-Ply Tissue, 23" x 24", 50/bg',
  groups: undefined
]

Why is it returning just "bg" as a match? I think it must be something with my parentheses grouping, but I can’t figure it out and have tried many configurations.

Thanks in advance!