filter

map

onlyMen

underTwenty

onlyNames

let people = [
  {name: 'გიორგი', age: 15, gender: 'male'},
  {name: 'ეკატერინე', age: 35, gender: 'female'},
  {name: 'დავითი', age: 75, gender: 'male'},
  {name: 'ნინო', age: 18, gender: 'female'},
  {name: 'თორნიკე', age: 11, gender: 'male'}
]
function onlyMen(human) {
  return human.gender == 'male'
}
function underTwenty(human) {
  return human.age < 20
}
function onlyNames(human) {
  return human.name
}
let onlyBoysNames = people.filter(onlyMen).filter(underTwenty).map(onlyNames)
document.write(onlyBoysNames)