Index: node_modules/d3-drag/src/event.js
===================================================================
--- node_modules/d3-drag/src/event.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-drag/src/event.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,28 @@
+export default function DragEvent(type, {
+  sourceEvent,
+  subject,
+  target,
+  identifier,
+  active,
+  x, y, dx, dy,
+  dispatch
+}) {
+  Object.defineProperties(this, {
+    type: {value: type, enumerable: true, configurable: true},
+    sourceEvent: {value: sourceEvent, enumerable: true, configurable: true},
+    subject: {value: subject, enumerable: true, configurable: true},
+    target: {value: target, enumerable: true, configurable: true},
+    identifier: {value: identifier, enumerable: true, configurable: true},
+    active: {value: active, enumerable: true, configurable: true},
+    x: {value: x, enumerable: true, configurable: true},
+    y: {value: y, enumerable: true, configurable: true},
+    dx: {value: dx, enumerable: true, configurable: true},
+    dy: {value: dy, enumerable: true, configurable: true},
+    _: {value: dispatch}
+  });
+}
+
+DragEvent.prototype.on = function() {
+  var value = this._.on.apply(this._, arguments);
+  return value === this._ ? this : value;
+};