Use Google Directions to render a route on a Google Map

Google Directions

import Deferred = require("dojo/Deferred");

class Navigation {

    private _directions: google.maps.DirectionsResult;
    private _ready: Deferred<Navigation>;

    constructor(args: {
        start?: any;
        end?: any;
        waypoints?: google.maps.Point[];
    }) {
        var service = new google.maps.DirectionsService();
        this._ready = new Deferred<Navigation>();

        var request = <google.maps.DirectionsRequest>{};
        request.avoidHighways = false;
        request.avoidTolls = false;
        request.optimizeWaypoints = true;
        request.provideRouteAlternatives = false;
        request.region = "us";
        request.travelMode = google.maps.TravelMode.DRIVING;
        request.unitSystem = google.maps.UnitSystem.IMPERIAL;

        if (args.waypoints) {
            request.waypoints = args.waypoints.map(w => {
                return {
                    location: w,
                    stopover: false
                };
            });
        }

        request.transitOptions = {
            arrivalTime: new Date(),
            departureTime: new Date()
        };

        request.origin = args.start;
        request.destination = args.end;

        service.route(request,(result, status) => {
            switch (status) {
                case google.maps.DirectionsStatus.INVALID_REQUEST:
                    break;
                case google.maps.DirectionsStatus.OK:
                    this._directions = result;
                    this._ready.resolve(this);
                    break;
                default:
                    break;
            }
        });


    }

    get then() {
        return this._ready.then;
    }

    render(map: google.maps.Map) {
        var options = <google.maps.DirectionsRendererOptions>{};
        options.map = map;
        options.directions = this._directions;
        var renderer = new google.maps.DirectionsRenderer(options);
        this._ready.then(() => {
            renderer.setDirections(this._directions);
        });
        // how to clear the directions?
    }

}

var map = new google.maps.Map(document.getElementById("map-canvas"), {
});

var directions = new Navigation({
    start: "Chicago, IL",
    end: "St Louis, MO"
});

directions.then(function () {
    directions.render(map);
});