key-gen.js

var fs = require("fs");
var helpers = require("./helpers");
var path = require("path");

function readFile(path, options) {
    return new Promise(function(resolve, reject) {
        fs.readFile(path, options, function(err, data) {
            if (err)  reject(err);
            else      resolve(data);
        })
    })
}

function loadData() {
    "use strict";
    var adjectivesPath = path.join(__dirname, "txt", "adjectives.txt");
    var nounPath = path.join(__dirname, "txt", "nouns.txt");

    return Promise.all([
       readFile(adjectivesPath).then(data => data.split(/\n|\r\n/).map(x => helpers.capitalizeFirstLetter(x).trim())),
       readFile(nounPath).then(data => data.split(/\n|\r\n/).map(x => helpers.capitalizeFirstLetter(x).trim())),
    ]);
}

var data = loadData(); // data is now a promise containing both arrays

function generateKey() {
    "use strict";
    return data.then(([adjectives, nouns]) => {
        var adjIndex = Math.floor(Math.random() * adjectives.length);
        var secondAdjIndex = Math.floor(Math.random() * adjectives.length);
        while (adjIndex === secondAdjIndex) {
            secondAdjIndex = Math.floor(Math.random() * adjectives.length);
        }
        var nounIndex = Math.floor(Math.random() * adjectives.length);
        return adjectives[adjIndex] + adjectives[secondAdjIndex] + nouns[nounIndex];
    })
}

// Now you use it as:
generateKey().then(thisIsYourKey => { doSomethingWithIt() })


module.exports = generateKey;