# SDL: emscripten: Fix handling of special HTML targets

**URL:** <https://discourse.libsdl.org/t/sdl-emscripten-fix-handling-of-special-html-targets/58420>\
**Category:** SDL Commits\
**Created:** [March 9, 2025, 1:15am UTC](https://discourse.libsdl.org/t/sdl-emscripten-fix-handling-of-special-html-targets/58420 "2025-03-09T01:15:46Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![SDLPushPostBot](https://discourse.libsdl.org/user_avatar/discourse.libsdl.org/sdlpushpostbot/32/4370_2.png) [@SDLPushPostBot](https://discourse.libsdl.org/u/SDLPushPostBot)\
**Post date:** [March 9, 2025, 1:15am UTC](https://discourse.libsdl.org/t/sdl-emscripten-fix-handling-of-special-html-targets/58420/1 "2025-03-09T01:15:46Z")

</div>

> <https://github.com/libsdl-org/SDL/commit/65cd2256c5542cba227e68902114c23500a74847>
>
> With ASAN enabled the existing code triggered null-pointer-dereference
> in the st…rcmp since EMSCRIPTEN\_EVENT\_TARGET\_WINDOW is a "fake" pointer
> with the value ((const char\*)2). In fixing this it was also noticed
> that using the #window/#document/#screen targets as mentioned in the
> docs fails since document.querySelector() returns null for them and we
> should instead be mapping them to the special HTML targets provided.

```diff
From 65cd2256c5542cba227e68902114c23500a74847 Mon Sep 17 00:00:00 2001
From: bobsayshilol <[EMAIL REDACTED]>
Date: Sat, 8 Mar 2025 03:29:07 +0000
Subject: [PATCH] emscripten: Fix handling of special HTML targets

With ASAN enabled the existing code triggered null-pointer-dereference
in the strcmp since EMSCRIPTEN_EVENT_TARGET_WINDOW is a "fake" pointer
with the value ((const char*)2). In fixing this it was also noticed
that using the #window/#document/#screen targets as mentioned in the
docs fails since document.querySelector() returns null for them and we
should instead be mapping them to the special HTML targets provided.
---
 src/video/emscripten/SDL_emscriptenevents.c | 37 ++++++++++++++-------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/src/video/emscripten/SDL_emscriptenevents.c b/src/video/emscripten/SDL_emscriptenevents.c
index 49a140f37e287..d9fa3c8fa3d67 100644
--- a/src/video/emscripten/SDL_emscriptenevents.c
+++ b/src/video/emscripten/SDL_emscriptenevents.c
@@ -1005,6 +1005,27 @@ static void Emscripten_unset_drag_event_callbacks(SDL_WindowData *data)
     }, data->canvas_id);
 }
 
+static const char *Emscripten_GetKeyboardTargetElement()
+{
+ const char *target = SDL_GetHint(SDL_HINT_EMSCRIPTEN_KEYBOARD_ELEMENT);
+
+ if (!target || !*target) {
+ return EMSCRIPTEN_EVENT_TARGET_WINDOW;
+ }
+
+ if (SDL_strcmp(target, "#none") == 0) {
+ return NULL;
+ } else if (SDL_strcmp(target, "#window") == 0) {
+ return EMSCRIPTEN_EVENT_TARGET_WINDOW;
+ } else if (SDL_strcmp(target, "#document") == 0) {
+ return EMSCRIPTEN_EVENT_TARGET_DOCUMENT;
+ } else if (SDL_strcmp(target, "#screen") == 0) {
+ return EMSCRIPTEN_EVENT_TARGET_SCREEN;
+ }
+
+ return target;
+}
+
 void Emscripten_RegisterEventHandlers(SDL_WindowData *data)
 {
     const char *keyElement;
@@ -1033,12 +1054,8 @@ void Emscripten_RegisterEventHandlers(SDL_WindowData *data)
     emscripten_set_pointerlockchange_callback(EMSCRIPTEN_EVENT_TARGET_DOCUMENT, data, 0, Emscripten_HandlePointerLockChange);
 
     // Keyboard events are awkward
- keyElement = SDL_GetHint(SDL_HINT_EMSCRIPTEN_KEYBOARD_ELEMENT);
- if (!keyElement || !*keyElement) {
- keyElement = EMSCRIPTEN_EVENT_TARGET_WINDOW;
- }
-
- if (SDL_strcmp(keyElement, "#none") != 0) {
+ keyElement = Emscripten_GetKeyboardTargetElement();
+ if (keyElement) {
         emscripten_set_keydown_callback(keyElement, data, 0, Emscripten_HandleKey);
         emscripten_set_keyup_callback(keyElement, data, 0, Emscripten_HandleKey);
         emscripten_set_keypress_callback(keyElement, data, 0, Emscripten_HandleKeyPress);
@@ -1094,12 +1111,8 @@ void Emscripten_UnregisterEventHandlers(SDL_WindowData *data)
 
     emscripten_set_pointerlockchange_callback(EMSCRIPTEN_EVENT_TARGET_DOCUMENT, NULL, 0, NULL);
 
- target = SDL_GetHint(SDL_HINT_EMSCRIPTEN_KEYBOARD_ELEMENT);
- if (!target || !*target) {
- target = EMSCRIPTEN_EVENT_TARGET_WINDOW;
- }
-
- if (SDL_strcmp(target, "#none") != 0) {
+ target = Emscripten_GetKeyboardTargetElement();
+ if (target) {
         emscripten_set_keydown_callback(target, NULL, 0, NULL);
         emscripten_set_keyup_callback(target, NULL, 0, NULL);
         emscripten_set_keypress_callback(target, NULL, 0, NULL);

```