Identify the marketing channel based referring domain information

identifyChannel.js

// channel_domain_mapping
var DOMAINS_NATURAL_SEARCH = ['www.google.', 'bing.', 
                              'search.yahoo.', '.yandex.'];
var DOMAINS_NATURAL_SOCIAL = ['facebook.com', 't.co', 'pinterest.', 'linkedin.com', 
                              'plus.google','instagram.com'];
var DOMAINS_REFERRING = ['.paypal.com','www.my-bank.com'];
                     
// Returns an array with the channel_id and the referring domain
function identifyChannel( channel_id , channel_domain_mapping , referrer) {
    if (referrer && referrer !== '') {
        // Extract the hostname portion of the referring URL.
        var ref_domain = get_domain_from_url(referrer); 
        var curr_domain = window.location.hostname;
        if (channel_id === REFERRING_DOMAIN) {
            // Referring Domains check: confirm that the referring domain
            // is present, different than the current domain and
            // does not match any domain present in the mapping
            if (curr_domain !== ref_domain) {
                var res = channel_domain_mapping.every(
                    x = > ref_domain.indexOf(x) === -1
                );
                if (res)
                    return [channel_id, ref_domain]
            }
        } else {
            // Referring Domains check: confirm that the referring domain
            // matches at least one domain present in the mapping
            var res = channel_domain_mapping.some(
                x = > (ref_domain.indexOf(x) > -1)
            );
            if (res)
                return [channel_id, ref_domain]
        }
    }
}