Add a way to remove a single event listener (#20983)

ChangeLog.md

@@ -20,6 +20,8 @@ See docs/process.md for more on how version tagging works.
 
 4.0.20 (in development)
 -----------------------
+- Added `emscripten_html5_remove_event_listener` function in `html5.h` in order to be
+  able to remove a single callback. (#25535)
 - Embind now requires C++17 or newer. See #24850.
 
 4.0.19 - 11/04/25

site/source/docs/api_reference/html5.h.rst

@@ -90,6 +90,52 @@ The ``useCapture`` parameter  maps to ``useCapture`` in `EventTarget.addEventLis
 
 Most functions return the result using the type :c:data:`EMSCRIPTEN_RESULT`. Zero and positive values denote success. Negative values signal failure. None of the functions fail or abort by throwing a JavaScript or C++ exception. If a particular browser does not support the given feature, the value :c:data:`EMSCRIPTEN_RESULT_NOT_SUPPORTED` will be returned at the time the callback is registered.
 
+Unregister function
+-------------------
+
+In order to unregister a single event handler callback, call the following function:
+
+  .. code-block:: cpp
+
+    EMSCRIPTEN_RESULT emscripten_html5_remove_event_listener(
+      const char *target,   // ID of the target HTML element.
+      void *userData,       // User-defined data (passed to the callback).
+      int eventTypeId,      // The event type ID (EMSCRIPTEN_EVENT_XXX).
+      void *callback        // Callback function.
+    );
+
+
+The ``target``, ``userData`` and ``callback`` parameters are the same parameters provided in ``emscripten_set_some_callback`` with the only difference being that, since this function applies to all types of callbacks, the type of ``callback`` is ``void *``.
+
+Note in particular that the value of ``userData`` will need to match with the call that was used to register the callback. If you are having trouble, double check the value of ``userData``.
+
+The ``eventTypeId`` represents the event type, the same Id received in the callback functions.
+
+  .. code-block:: cpp
+
+    // Example
+
+    bool my_mouse_callback_1(int eventType, const EmscriptenMouseEvent *mouseEvent, void *userData) {
+      // ...
+    }
+
+    bool my_mouse_callback_2(int eventType, const EmscriptenMouseEvent *mouseEvent, void *userData) {
+      // ...
+    }
+
+    void main() {
+
+      // 1. set callbacks for mouse down and mouse move
+      emscripten_set_mousedown_callback("#mydiv", 0, my_mouse_callback_1);
+      emscripten_set_mousedown_callback("#mydiv", (void *) 34, my_mouse_callback_2);
+      emscripten_set_mousemove_callback("#mydiv", 0, my_mouse_callback_1);
+
+      // 2. remove these callbacks
+      emscripten_html5_remove_event_listener("#mydiv", 0, EMSCRIPTEN_EVENT_MOUSEDOWN, my_mouse_callback_1);
+      emscripten_html5_remove_event_listener("#mydiv", (void *) 34, EMSCRIPTEN_EVENT_MOUSEDOWN, my_mouse_callback_2);
+      emscripten_html5_remove_event_listener("#mydiv", 0, EMSCRIPTEN_EVENT_MOUSEMOVE, my_mouse_callback_1);
+    }
+
 
 Callback functions
 ------------------

src/lib/libhtml5.js

@@ -205,6 +205,25 @@ var LibraryHTML5 = {
       return {{{ cDefs.EMSCRIPTEN_RESULT_SUCCESS }}};
     },
 
+    removeSingleHandler(eventHandler) {
+      if (!eventHandler.target) {
+#if ASSERTIONS
+        err('removeSingleHandler: the target element for event handler registration does not exist, when processing the following event handler registration:');
+        console.dir(eventHandler);
+#endif
+        return {{{ cDefs.EMSCRIPTEN_RESULT_UNKNOWN_TARGET }}};
+      }
+      for (var i = 0; i < JSEvents.eventHandlers.length; ++i) {
+        if (JSEvents.eventHandlers[i].target === eventHandler.target
+          && JSEvents.eventHandlers[i].eventTypeId === eventHandler.eventTypeId
+          && JSEvents.eventHandlers[i].callbackfunc === eventHandler.callbackfunc
+          && JSEvents.eventHandlers[i].userData === eventHandler.userData) {
+          JSEvents._removeHandler(i--);
+        }
+      }
+      return {{{ cDefs.EMSCRIPTEN_RESULT_SUCCESS }}};
+    },
+
 #if PTHREADS
     getTargetThreadForEventCallback(targetThread) {
       switch (targetThread) {
@@ -295,6 +314,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target: findEventTarget(target),
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: keyEventHandlerFunc,
       useCapture
@@ -409,6 +430,18 @@ var LibraryHTML5 = {
   },
 #endif
 
+  emscripten_html5_remove_event_listener__proxy: 'sync',
+  emscripten_html5_remove_event_listener__deps: ['$JSEvents', '$findEventTarget'],
+  emscripten_html5_remove_event_listener: (target, userData, eventTypeId, callback) => {
+    var eventHandler = {
+      target: findEventTarget(target),
+      userData,
+      eventTypeId,
+      callbackfunc: callback,
+    };
+    return JSEvents.removeSingleHandler(eventHandler);
+  },
+
   emscripten_set_keypress_callback_on_thread__proxy: 'sync',
   emscripten_set_keypress_callback_on_thread__deps: ['$registerKeyEventCallback'],
   emscripten_set_keypress_callback_on_thread: (target, userData, useCapture, callbackfunc, targetThread) =>
@@ -499,6 +532,8 @@ var LibraryHTML5 = {
       allowsDeferredCalls: eventTypeString != 'mousemove' && eventTypeString != 'mouseenter' && eventTypeString != 'mouseleave', // Mouse move events do not allow fullscreen/pointer lock requests to be handled in them!
 #endif
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: mouseEventHandlerFunc,
       useCapture
@@ -592,6 +627,8 @@ var LibraryHTML5 = {
       allowsDeferredCalls: true,
 #endif
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: wheelHandlerFunc,
       useCapture
@@ -664,6 +701,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target,
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: uiEventHandlerFunc,
       useCapture
@@ -708,6 +747,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target: findEventTarget(target),
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: focusEventHandlerFunc,
       useCapture
@@ -765,6 +806,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target: findEventTarget(target),
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: deviceOrientationEventHandlerFunc,
       useCapture
@@ -835,6 +878,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target: findEventTarget(target),
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: deviceMotionEventHandlerFunc,
       useCapture
@@ -917,6 +962,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target,
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: orientationChangeEventHandlerFunc,
       useCapture
@@ -1024,6 +1071,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target,
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: fullscreenChangeEventhandlerFunc,
       useCapture
@@ -1522,6 +1571,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target,
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: pointerlockChangeEventHandlerFunc,
       useCapture
@@ -1566,6 +1617,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target,
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: pointerlockErrorEventHandlerFunc,
       useCapture
@@ -1716,6 +1769,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target,
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: visibilityChangeEventHandlerFunc,
       useCapture
@@ -1831,6 +1886,8 @@ var LibraryHTML5 = {
       allowsDeferredCalls: eventTypeString == 'touchstart' || eventTypeString == 'touchend',
 #endif
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: touchEventHandlerFunc,
       useCapture
@@ -1914,6 +1971,8 @@ var LibraryHTML5 = {
       allowsDeferredCalls: true,
 #endif
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: gamepadEventHandlerFunc,
       useCapture
@@ -2000,6 +2059,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target: findEventTarget(target),
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: beforeUnloadEventHandlerFunc,
       useCapture
@@ -2050,6 +2111,8 @@ var LibraryHTML5 = {
     var eventHandler = {
       target: battery,
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: batteryEventHandlerFunc,
       useCapture

src/lib/libhtml5_webgl.js

@@ -440,6 +440,8 @@ var LibraryHtml5WebGL = {
     var eventHandler = {
       target: findEventTarget(target),
       eventTypeString,
+      eventTypeId,
+      userData,
       callbackfunc,
       handlerFunc: webGlEventHandlerFunc,
       useCapture

src/lib/libsigs.js

@@ -666,6 +666,7 @@ sigs = {
   emscripten_has_threading_support__sig: 'i',
   emscripten_hide_mouse__sig: 'v',
   emscripten_html5_remove_all_event_listeners__sig: 'v',
+  emscripten_html5_remove_event_listener__sig: 'ippip',
   emscripten_idb_async_clear__sig: 'vpppp',
   emscripten_idb_async_delete__sig: 'vppppp',
   emscripten_idb_async_exists__sig: 'vppppp',

system/include/emscripten/html5.h

@@ -420,6 +420,8 @@ EMSCRIPTEN_RESULT emscripten_get_element_css_size(const char *target __attribute
 
 void emscripten_html5_remove_all_event_listeners(void);
 
+EMSCRIPTEN_RESULT emscripten_html5_remove_event_listener(const char *target __attribute__((nonnull)), void *userData, int eventTypeId, void *callback __attribute__((nonnull)));
+
 #define EM_CALLBACK_THREAD_CONTEXT_MAIN_RUNTIME_THREAD ((pthread_t)0x1)
 #define EM_CALLBACK_THREAD_CONTEXT_CALLING_THREAD ((pthread_t)0x2)
 

test/codesize/test_codesize_cxx_ctors1.json

@@ -1,10 +1,10 @@
 {
   "a.out.js": 19670,
   "a.out.js.gz": 8152,
-  "a.out.nodebug.wasm": 129456,
-  "a.out.nodebug.wasm.gz": 49187,
-  "total": 149126,
-  "total_gz": 57339,
+  "a.out.nodebug.wasm": 129503,
+  "a.out.nodebug.wasm.gz": 49248,
+  "total": 149173,
+  "total_gz": 57400,
   "sent": [
     "__cxa_throw",
     "_abort_js",

test/codesize/test_codesize_cxx_ctors2.json

@@ -1,10 +1,10 @@
 {
   "a.out.js": 19647,
   "a.out.js.gz": 8139,
-  "a.out.nodebug.wasm": 128883,
-  "a.out.nodebug.wasm.gz": 48829,
-  "total": 148530,
-  "total_gz": 56968,
+  "a.out.nodebug.wasm": 128930,
+  "a.out.nodebug.wasm.gz": 48886,
+  "total": 148577,
+  "total_gz": 57025,
   "sent": [
     "__cxa_throw",
     "_abort_js",

test/codesize/test_codesize_cxx_except.json

@@ -1,10 +1,10 @@
 {
   "a.out.js": 23325,
   "a.out.js.gz": 9128,
-  "a.out.nodebug.wasm": 171264,
-  "a.out.nodebug.wasm.gz": 57309,
-  "total": 194589,
-  "total_gz": 66437,
+  "a.out.nodebug.wasm": 171311,
+  "a.out.nodebug.wasm.gz": 57348,
+  "total": 194636,
+  "total_gz": 66476,
   "sent": [
     "__cxa_begin_catch",
     "__cxa_end_catch",

test/codesize/test_codesize_cxx_except_wasm.json

@@ -1,10 +1,10 @@
 {
   "a.out.js": 19486,
   "a.out.js.gz": 8077,
-  "a.out.nodebug.wasm": 144620,
-  "a.out.nodebug.wasm.gz": 54869,
-  "total": 164106,
-  "total_gz": 62946,
+  "a.out.nodebug.wasm": 144667,
+  "a.out.nodebug.wasm.gz": 54907,
+  "total": 164153,
+  "total_gz": 62984,
   "sent": [
     "_abort_js",
     "_tzset_js",

test/codesize/test_codesize_cxx_except_wasm_legacy.json

@@ -1,10 +1,10 @@
 {
   "a.out.js": 19555,
   "a.out.js.gz": 8099,
-  "a.out.nodebug.wasm": 142209,
-  "a.out.nodebug.wasm.gz": 54320,
-  "total": 161764,
-  "total_gz": 62419,
+  "a.out.nodebug.wasm": 142256,
+  "a.out.nodebug.wasm.gz": 54366,
+  "total": 161811,
+  "total_gz": 62465,
   "sent": [
     "_abort_js",
     "_tzset_js",

test/codesize/test_codesize_cxx_lto.json

@@ -1,10 +1,10 @@
 {
   "a.out.js": 19009,
   "a.out.js.gz": 7829,
-  "a.out.nodebug.wasm": 106443,
-  "a.out.nodebug.wasm.gz": 42551,
-  "total": 125452,
-  "total_gz": 50380,
+  "a.out.nodebug.wasm": 106439,
+  "a.out.nodebug.wasm.gz": 42591,
+  "total": 125448,
+  "total_gz": 50420,
   "sent": [
     "a (emscripten_resize_heap)",
     "b (_setitimer_js)",

test/codesize/test_codesize_cxx_mangle.json

@@ -1,10 +1,10 @@
 {
   "a.out.js": 23375,
   "a.out.js.gz": 9148,
-  "a.out.nodebug.wasm": 235290,
-  "a.out.nodebug.wasm.gz": 78915,
-  "total": 258665,
-  "total_gz": 88063,
+  "a.out.nodebug.wasm": 235343,
+  "a.out.nodebug.wasm.gz": 78952,
+  "total": 258718,
+  "total_gz": 88100,
   "sent": [
     "__cxa_begin_catch",
     "__cxa_end_catch",

test/codesize/test_codesize_cxx_noexcept.json

@@ -1,10 +1,10 @@
 {
   "a.out.js": 19670,
   "a.out.js.gz": 8152,
-  "a.out.nodebug.wasm": 131873,
-  "a.out.nodebug.wasm.gz": 50187,
-  "total": 151543,
-  "total_gz": 58339,
+  "a.out.nodebug.wasm": 131920,
+  "a.out.nodebug.wasm.gz": 50242,
+  "total": 151590,
+  "total_gz": 58394,
   "sent": [
     "__cxa_throw",
     "_abort_js",