Split the sentences by ‘,’ and remove surrounding spaces

I have this code:

var r = /(?:^s*([^s]*)s*)(?:,s*([^s]*)s*){0,}$/
var s = "   a   ,  b  , c "
var m = s.match(r)
m => ["   a   ,  b  , c ", "a", "c"]

Looks like the whole string has been matched, but where has "b" gone? I would rather expect to get:

["   a   ,  b  , c ", "a", "b", "c"]

so that I can do m.shift() with a result like s.split(',') but also with whitespaces removed.

Do I have a mistake in the regexp or do I misunderstand String.prototype.match?

Answer

so finally i went with /(?=S)[^,]+?(?=s*(,|$))/g, which provides exactly what i need: all sentences split by ‘,’ without surrounding spaces.

'       a,    OMG     abc b a b, d o WTF        foo     '.
  match( /(?=S)[^,]+?(?=s*(,|$))/g )
=> ["a", "OMG     abc b a b", "d o WTF        foo"]

many thanks!