gistfile1.txt

function bingap(n) {
  const binary = (n >>> 0).toString(2);
  const f1 = new RegExp(/1?0+1?/, 'g');
  const f2 = new RegExp(/1(0+)1/);
  return binary.match(f1)
               .filter(r1 => r1.match(f2))
               .reduce((acc, n) => acc > n.length - 2 ? acc : n.length - 2, 0)
}

console.log(bingap(42));
console.log(bingap(48));
console.log(bingap(49));