How to use the geolib.longitude function in geolib

function geocode(location, callback) {
  var lonLat = [geolib.longitude(location), geolib.latitude(location)].join(',');

  // Function for requesting a reversed geocode location if we have no cache entry
  function requestApi() {
    var apiURLObject = url.parse(config.mapbox.api_url, true),
      path = ['geocode', config.mapbox.geocoding_index];

    path.push(lonLat);

    apiURLObject.pathname += '/' + path.join('/') + '.json';
    apiURLObject.query.access_token = clientConfig.mapbox.token;

    var options = {
      url: url.format(apiURLObject),
      gzip: true
    };