Node JS code to load JSON document with countries and prepare some useful Sets with unique collections of data from the JSON document

neo4j-node.js

var countriesDocumentURL = "https://raw.githubusercontent.com/mledoze/countries/master/countries.json"
request(countriesDocumentURL, async function (error, response, body) {

    var countries = JSON.parse(body)
    // get unique region values (see: https://codeburst.io/javascript-array-distinct-5edc93501dc4)
    // take all elements in the countries array, for each of them: take the region element; create a Set of all the resulting region values (a Set contains unique elements)
    var regions = [...new Set(countries.map(country => country.region))]
    var subregions = [...new Set(countries.map(country => country.subregion))]
    // see https://stackoverflow.com/questions/39837678/why-no-array-prototype-flatmap-in-javascript for this flatMap function
    const flatMap = (f, xs) =>
        xs.reduce((acc, x) =>
            acc.concat(f(x)), [])

    // take all elements in the countries array, for each of them: take the array of languages ); create one big array of all small arrays of languages (this is what the flatmap does) and turn that big array into a Set (of unique language values)
    var languages = [...new Set(flatMap(country => Object.values(country.languages), countries))]