index.js

'use strict';
let slds = {
    ar: require('./countries/ar.js'),
    at: require('./countries/at.js'),
    au: require('./countries/au.js'),
    br: require('./countries/br.js'),
    mt: require('./countries/mt.js'),
    mx: require('./countries/mx.js'),
    nz: require('./countries/nz.js'),
    sg: require('./countries/sg.js'),
    uk: require('./countries/uk.js'),
    za: require('./countries/za.js')
};

/**
 * Check whether a given domain name is a top level domain.
 * @param domain_name {string}
 * @returns {boolean}
 */
module.exports = (domain_name) => {
    // Convert a.b.c.d => ['d', 'c'] (only interested in last two elements in reverse order)
    const niamod = domain_name.split('.').reverse().splice(0, 2);
    const sld = slds[niamod[0]];
    return !!sld && sld.indexOf(niamod[1]) >= 0;
}