extractBetween js function

function extractBetween(str, starts, ends) {
  var p=str.indexOf(starts)
  if (p != -1) {
      p+=starts.length
      var p1=str.indexOf(ends, p)
      if (p1 != -1) {
          return str.slice(p, p1)
      }
  }
  return false
}

// >>> extractBetween('<h1>Заголовок</h1>', '<h1>', '</h1>')
// "Заголовок"