How to get total driving distance with Google Maps API V3?

As per Leniel’s answer:

var totalDistance = 0;
var totalDuration = 0;
var legs = directionsResult.routes[0].legs;
for(var i=0; i<legs.length; ++i) {
    totalDistance += legs[i].distance.value;
    totalDuration += legs[i].duration.value;
}
$('#distance').text(totalDistance);
$('#duration').text(totalDuration);

Actually, this works just fine too, if you don’t have any waypoints:

$('#distance').text(directionsResult.routes[0].legs[0].distance.text);
$('#duration').text(directionsResult.routes[0].legs[0].duration.text);

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Here’s a fuller example using lodash. Shouldn’t be too hard to replace flatBy and sum if you’re not using it.

/**
 * Computes the total driving distance between addresses. Result in meters.
 *
 * @param {string[]} addresses Array of address strings. Requires two or more.
 * @returns {Promise} Driving distance in meters
 */
export default function calculateDistance(addresses) {
    return new Promise((resolve, reject) => {
        if(addresses.length < 2) {
            return reject(new Error(`Distance calculation requires at least 2 stops, got ${addresses.length}`));
        }

        const {TravelMode, DirectionsService, DirectionsStatus} = google.maps;

        const directionsService = new DirectionsService;
        const origin = addresses.shift();
        const destination = addresses.pop();
        const waypoints = addresses.map(stop => ({location: stop}));

        directionsService.route({
            origin,
            waypoints,
            destination,
            travelMode: TravelMode.DRIVING,
        }, (response, status) => {
            if(status === DirectionsStatus.OK) {
                let distances = _.flatMap(response.routes, route => _.flatMap(route.legs, leg => leg.distance.value));

                return resolve(_.sum(distances));
            } else {
                return reject(new Error(status));
            }
        });
    });
}

Remember to include the Google Maps API:

<script src="https://maps.googleapis.com/maps/api/js?key=API_KEY&libraries=places"></script>

Also, I’m pretty sure their ToS require you to display a Google Map too.