Mapbox's demo of swiping between layers has no example of how to implement the effect with L.LayerGroup. [layerGroup].eachLayer()
would be the obvious call, but I couldn't get it to work. Fortunately, it was a simple matter of determining the length of the layer group, and iterating through.
var droneArray = droneLayers.getLayers();
function clip() {
var nw = map.containerPointToLayerPoint([0, 0]),
se = map.containerPointToLayerPoint(map.getSize()),
clipX = nw.x + (se.x - nw.x) * range.value;