From e9f489a6292c453d900284523e4ff0c0f67333a0 Mon Sep 17 00:00:00 2001
From: Jesper Alf Dam <jdam@vitalimages.com>
Date: Fri, 16 Aug 2019 14:27:12 +0200
Subject: [PATCH] Avoid recursion in Alt check on Firefox

The Firefox workaround which checks for missing Alt key events may
synthesise new KeyboardEvents. On these events, checkAlt should not be
recursively triggered. Otherwise, we get "too much recursion" errors
whenever the Alt key is pressed.
---
 core/input/keyboard.js | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/core/input/keyboard.js b/core/input/keyboard.js
index 9dbc8d6e..d9c271c9 100644
--- a/core/input/keyboard.js
+++ b/core/input/keyboard.js
@@ -301,6 +301,9 @@ export default class Keyboard {
 
     // Firefox Alt workaround, see below
     _checkAlt(e) {
+        if (e.skipCheckAlt) {
+            return;
+        }
         if (e.altKey) {
             return;
         }
@@ -315,6 +318,7 @@ export default class Keyboard {
             const event = new KeyboardEvent('keyup',
                                             { key: downList[code],
                                               code: code });
+            event.skipCheckAlt = true;
             target.dispatchEvent(event);
         });
     }