currencies.js

fetch(`https://restcountries.eu/rest/v1/all`)
.then((res) => {
  return res.json()
})
.then((values) =>{
  let array = values
              .map(x => {return x.currencies[0];})
              //.filter((v, i, a) => a.indexOf(v) === i);  // filter unique
  array = Array.from(new Set(array)) // filter ES6 way
  console.log(array)
})