sort_object_by_age_field.js

function compareAges(a,b) {
  if (a.age < b.age)
    return -1;
  if (a.age > b.age)
    return 1;
  return 0;
}

let people = [{ name: 'John', age: '21' } , { name: 'Nick', age: 12 }, { name: 'Old' , age: 99 }];
people.sort(compareAges);