@gmaclennan

I've updated the lib so that getContainer is replaced by getPane (leaflet 1.9)

const sbs = L.control.sideBySide([], []).addTo(this.map);
const layer1 = L.geoJSON(MYGEOJSONOBJECT01, { style: { color: 'green', weight: 2, opacity: 1 } }).addTo(this.map);
const layer2 = L.geoJSON(MYGEOJSONOBJECT02, { style: { color: 'red', weight: 2, opacity: 1 } }).addTo(this.map);
sbs.setLeftLayers(layer1);
sbs.setRightLayers(layer2);

Both layers are on the right pane...

I've tried setting them up directly in the sideBySide() function for the same result.

EDIT: setxxxLayers individually work, but not both at the same time. So I either get left pane working with blank right pane or the other way around.