In leaflet/mapbox, why can't I set the duration of `map.fitBounds`?

Question

I tried this:

map.fitBounds(L.polyline([L.latLng(40,9), L.latLng(1,2)]).getBounds(), {
  padding: [50, 50],
  maxZoom: 17,
  animate: true,
  duration: 10
});

I expect the animation to take 10 seconds to complete, but it completes very fast.. Does anyone have ideas about how to make the duration longer for fitBounds?

Answer 1

It should be set as:

map.fitBounds(bounds, {
    padding: [50, 50],
    maxZoom: 18,
    animate: true,
    pan: {
        duration: 10
    }
});