tracarRotaMaps.js

directionsService = new google.maps.DirectionsService();
directionsDisplay = new google.maps.DirectionsRenderer();
directionsDisplay.setMap(map);
var request = {
    origin: lojas[0].location, 
    destination: lojas[1].location, 
    travelMode: google.maps.TravelMode.DRIVING
};

directionsService.route(request, function (result, status) {
    if (status == google.maps.DirectionsStatus.OK) {
        directionsDisplay.setDirections(result);
        directionsDisplay.setOptions({ suppressMarkers: true });
    } else {
        alert('error');
    }
});