Finding matches using regular expression

Question

How to find the length of consecutive zeros that is surrounded by ones at both ends of a binary?

For example, in 10010001 the 2 matches are 1001 and 10001

• 1001 the length of zeroes is 2
• 10001 the length of zeroes is 3

I used match which returned only the last one i.e. 10001.

'1010001'.match(/1(0+)1$/g)

Answer 1

You need lookahead assertions here:

console.log('1010001'.match(/10+(?=1)/g).map(function(x) {
   return x.length - 1;
}));