JavaScript regex global flag doesn't return all occurences

Question

I have a binary representation of a decimal:

1000010001

I want to match a sequence of consecutive zeros that is surrounded by ones at both ends, 10001.

So in my string there are two such occurrences:

100001
10001

But for some reason match with g returns only the first:

'1000010001'.match(/(?:10+1)+/ig)
> ["100001"]

Why not both? How to make it return all occurrences?

The first match "consumes" the second `1` digit. You could back up the regex by 1 after each match if you did the matching in a loop. — Pointy, Dec 09 '17 at 19:24
There is a dupe for this somewhere. I'm searching.... Bottom line is: when `100001` is matched, what left in the string is `0001` so applying the regex on the rest won't match. — ibrahim mahrir, Dec 09 '17 at 19:28

score 2 · Accepted Answer · answered Dec 09 '17 at 19:24

The matches consume characters, so after the first match, the string becomes 0001 and thus doesn't match the pattern anymore; You can turn the second 1 in the pattern into a look ahead assertion which doesn't consume characters, then add 1 to each match later:

var s = '1000010001';

console.log(
  s.match(/10+(?=1)/g).map(x => x + '1')
)

JavaScript regex global flag doesn't return all occurences

1 Answers1