what3words API authentication with jQuery

what3words-jquery.js

var json = (function() {
  var json = null;
  $.ajax({
    'async': true,
    'global': false,
    'url': "./config.json",
    'dataType': "json",
    'success': function (data) {
      json = data;
    }
  });
  return json;
})();

var key = json.what3words.key;

var options = {
  key: key
  lang: 'en'
};
var w3w = new What3words(options);