_index.js

var twilio = require('twilio');
var primality = require('primality');
var countries = require('./countries');

const accountSid = process.env.TWILIO_AC_SID;
const authToken = process.env.TWILIO_AUTH_TOKEN;
var client = require('twilio')(accountSid, authToken);

function getRandomInt(min, max) {
  // max and min numst be integers
  return Math.floor(Math.random() * (max - min)) + min;
}

function getPrimePhoneNumbers(isoCountry, areaCode) {

  // An array to hold all the promises we get from Twilio API requests
  let promises = [];
  // Get the length of the country code so we know what to cut off from the number
  let countryCodeLen = countries[isoCountry].code.length;

  for (let i = 0; i < 20; i++) {
    // Make a call to the available phone numbers API for the US
    let twilioPromise = client.availablePhoneNumbers(isoCountry).local.list({
      Contains: getRandomInt(10,99),
      areaCode: areaCode
    });

    promises.push(twilioPromise);
  }

  // phonePromise will resolve when all of the promises in the promises array resolve
  let phonePromise = Promise.all(promises);

  // assign the resolution of phonePromise to a variable
  primeNumberPromise = phonePromise.then(data => {
    var verifiedPrimes = [];

    data.forEach(twilioObject => {
      twilioObject.available_phone_numbers.forEach(e => {       
        if (primality(e.phone_number.slice(countryCodeLen)) 
            && !verifiedPrimes.includes(e.phone_number.slice(countryCodeLen))) {
          // Slice off the country code using the length calculated above
          verifiedPrimes.push(e.phone_number.slice(countryCodeLen));
        }
      })
    });

    return verifiedPrimes;
  });

  return primeNumberPromise;
}

console.log('US numbers:');
getPrimePhoneNumbers('US', 650).then(data => console.log(data));

// Search by area code only works for US and Canada. Twilio just ignores it for other countries
console.log('UK numbers:');
getPrimePhoneNumbers('GB').then(data => console.log(data)); 

countries.js

module.exports = {
	US: {
		name: "United States",
		code: "+1",
	},
	AU: {
		name: "Australia",
		code: "+61",
	},
	AT: {
		name: "Austria",
		code: "+43",
	},
	BE: {
		name: "Belgium",
		code: "+32",
	},
	BR: {
		name: "Brazil",
		code: "+55",
	},
	BG: {
		name: "Bulgaria",
		code: "+359",
	},
	CA: {
		name: "Canada",
		code: "+1",
	},
	CL: {
		name: "Chile",
		code: "+56",
	},
	CY: {
		name: "Cyprus",
		code: "+357",
	},
	CZ: {
		name: "Czech Republic",
		code: "+420",
	},
	DK: {
		name: "Denmark",
		code: "+45",
	},
	DO: {
		name: "Dominican Republic",
		code: "+1829",
	},
	SV: {
		name: "El Salvador",
		code: "+503",
	},
	EE: {
		name: "Estonia",
		code: "+372",
	},
	FI: {
		name: "Finland",
		code: "+358",
	},
	FR: {
		name: "France",
		code: "+33",
	},
	DE: {
		name: "Germany",
		code: "+49",
	},
	GR: {
		name: "Greece",
		code: "+30",
	},
	HK: {
		name: "Hong Kong",
		code: "+852",
	},
	HU: {
		name: "Hungary",
		code: "+36",
	},
	ID: {
		name: "Indonesia",
		code: "+62",
	},
	IE: {
		name: "Ireland",
		code: "+353",
	},
	IL: {
		name: "Israel",
		code: "+972",
	},
	IT: {
		name: "Italy",
		code: "+39",
	},
	JP: {
		name: "Japan",
		code: "+81",
	},
	LV: {
		name: "Latvia",
		code: "+371",
	},
	LT: {
		name: "Lithuania",
		code: "+370",
	},
	LU: {
		name: "Luxembourg",
		code: "+352",
	},
	MT: {
		name: "Malta",
		code: "+356",
	},
	MX: {
		name: "Mexico",
		code: "+52",
	},
	NL: {
		name: "Netherlands",
		code: "+31",
	},
	NZ: {
		name: "New Zealand",
		code: "+64",
	},
	NO: {
		name: "Norway",
		code: "+47",
	},
	PE: {
		name: "Peru",
		code: "+51",
	},
	PL: {
		name: "Poland",
		code: "+48",
	},
	PT: {
		name: "Portugal",
		code: "+351",
	},
	PR: {
		name: "Puerto Rico",
		code: "+1",
	},
	RO: {
		name: "Romania",
		code: "+40",
	},
	SK: {
		name: "Slovakia",
		code: "+421",
	},
	ZA: {
		name: "South Africa",
		code: "+27",
	},
	ES: {
		name: "Spain",
		code: "+34",
	},
	SE: {
		name: "Sweden",
		code: "+46",
	},
	CH: {
		name: "Switzerland",
		code: "+41",
	},
	GB: {
		name: "United Kingdom",
		code: "+44",
	}
}