fix event.relatedTarget fallback logic for firefox (#19607)

* fix event.relatedTarget fallback logic for firefox * check if relatedTarget is undefined for fallback
2020-08-14 08:05:53 -04:00 · 2020-08-14 08:05:53 -04:00 · fe6d05229f
parent 1d5e10f703
commit fe6d05229f
1 changed files with 5 additions and 5 deletions
--- a/packages/react-dom/src/events/SyntheticEvent.js
+++ b/packages/react-dom/src/events/SyntheticEvent.js
@ -170,12 +170,12 @@ export const MouseEventInterface = {
  button: 0,
  buttons: 0,
  relatedTarget: function(event) {
-    return (
-      event.relatedTarget ||
-      (event.fromElement === event.srcElement
+    if (event.relatedTarget === undefined)
+      return event.fromElement === event.srcElement
        ? event.toElement
-        : event.fromElement)
-    );
+        : event.fromElement;
+
+    return event.relatedTarget;
  },
  movementX: function(event) {
    if ('movementX' in event) {