mapped.js

const officers = [
    {id: 1, name: 'Cpt Brown', country: 'NZ'},
    {id: 2, name: 'Lt Fredrick', country: 'USA'},
    {id: 3, name: 'Sgt Deaken', country: 'NZ'},
    {id: 4, name: 'Lt Smoller', country: 'CAN'},
    {id: 5, name: 'Cpt Kincaid', country: 'USA'}
]

// var ids = officers.map(function(o) {
//     return o.id
// })

const ids = officers.map((o) => {
    return o.id
})

map and arrow function

const ids = officers.map(o => o.id)