var selectFirstOnEnter = function(input) {  // store the original event binding function
    var _addEventListener = (input.addEventListener) ? input.addEventListener : input.attachEvent;
    function addEventListenerWrapper(type, listener) {  // Simulate a 'down arrow' keypress on hitting 'return' when no pac suggestion is selected, and then trigger the original listener.
        if (type == "keydown") { 
            var orig_listener = listener;
            listener = function(event) {
                var suggestion_selected = $(".pac-item-selected").length > 0;
                if (event.which == 13 && !suggestion_selected) { 
                    var simulated_downarrow = $.Event("keydown", {keyCode: 40, which: 40}); 
                    orig_listener.apply(input, [simulated_downarrow]); 
                }
                orig_listener.apply(input, [event]);
            };
        }
        _addEventListener.apply(input, [type, listener]); // add the modified listener
    }
    if (input.addEventListener) { 
        input.addEventListener = addEventListenerWrapper; 
    } else if (input.attachEvent) { 
        input.attachEvent = addEventListenerWrapper; 
    }
}