Google Maps union multiple polygon within BackboneJS view

union-bounds.js

var MapView = Backbone.View.extend({
    /**
     * Combine the boundaries of a list of Polygons into one boundary.
     *
     * The resulting boundary may for example be used in Map.fitBounds().
     *
     * @param {google.maps.Polygon[]}
     *
     * @return {google.maps.LatLngBounds}
     */
    unionBounds: function(polygons) {
        return _.reduce(polygons, function(bounds, polygon) {
            return bounds.union(polygon.getBounds());
        }, new google.maps.LatLngBounds());
    }
});

// example getBounds method
google.maps.Polygon.prototype.getBounds = function() {
    var bounds = new google.maps.LatLngBounds();

    this.getPaths().forEach(function(path) {
        path.forEach(function(point) {
            bounds.extend(point);
        });
    });

    return bounds;
};