Index: node_modules/d3-selection/src/sourceEvent.js
===================================================================
--- node_modules/d3-selection/src/sourceEvent.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-selection/src/sourceEvent.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,5 @@
+export default function(event) {
+  let sourceEvent;
+  while (sourceEvent = event.sourceEvent) event = sourceEvent;
+  return event;
+}