let element = document.getElementById('selected')

const prevAll = (element) => { 
  let all = []
  while (element = element.previousElementSibling) {
    all.push(element)
  }
  
  return all
}

const nextAll = element => {
  let all = []
  while (element = element.nextElementSibling) {
    all.push(element)
  }
  
  return all
}


console.log(prevAll(element))
console.log(nextAll(element))
console.log(element)