// Control implemented as ES6 class
                    class HelloWorldControl {
                        onAdd(map) {
                            this._map = map;
                            this._container = document.createElement('div');
                            this._container.className = 'mapboxgl-ctrl';
                            this._container.textContent = 'Hello, world';
                            return this._container;
                        }

                        onRemove() {
                            this._container.parentNode.removeChild(this._container);
                            this._map = undefined;
                        }
                    }

                    // Control implemented as ES5 prototypical class
                    function HelloWorldControl() { }

                    HelloWorldControl.prototype.onAdd = function(map) {
                        this._map = map;
                        this._container = document.createElement('div');
                        this._container.className = 'mapboxgl-ctrl';
                        this._container.textContent = 'Hello, world';
                        return this._container;
                    };

                    HelloWorldControl.prototype.onRemove = function () {
                        this._container.parentNode.removeChild(this._container);
                        this._map = undefined;
                    };