const princesses = [
  {name: 'Rapunzel', age: 18},
  {name: 'Mulan', age: 16},
  {name: 'Anna', age: 18},
  {name: 'Moana', age: 16}
];

let names = princesses.map(function(item) {
  return item.name;
});

console.log(names);