From 6fd51cfdc0e6facabf1c0631a6ff33f4ef25839a Mon Sep 17 00:00:00 2001
From: Pierre Tachoire <pierre@lightpanda.io>
Date: Fri, 27 Feb 2026 14:47:43 +0100
Subject: [PATCH] Set a null attribute listener must remove existing value

---
 .../tests/element/html/event_listeners.html   |  23 ++
 src/browser/webapi/element/Html.zig           | 205 +++++++++---------
 2 files changed, 130 insertions(+), 98 deletions(-)

diff --git a/src/browser/tests/element/html/event_listeners.html b/src/browser/tests/element/html/event_listeners.html
index 58394b7c..73b85631 100644
--- a/src/browser/tests/element/html/event_listeners.html
+++ b/src/browser/tests/element/html/event_listeners.html
@@ -143,6 +143,29 @@
 }
 </script>
 
+<script id="js_setter_null_clears_listener">
+{
+    // Setting an event handler property to null must silently clear it (not throw).
+    // Browsers also accept undefined and non-function values without throwing.
+    const div = document.createElement('div');
+
+    div.onload = () => 42;
+    testing.expectEqual('function', typeof div.onload);
+
+    // Setting to null removes the listener; getter returns null
+    div.onload = null;
+    testing.expectEqual(null, div.onload);
+
+    div.onerror = () => {};
+    div.onerror = null;
+    testing.expectEqual(null, div.onerror);
+
+    div.onclick = () => {};
+    div.onclick = null;
+    testing.expectEqual(null, div.onclick);
+}
+</script>
+
 <script id="different_event_types_independent">
 {
     // Test that different event types are stored independently
diff --git a/src/browser/webapi/element/Html.zig b/src/browser/webapi/element/Html.zig
index 6d2cf086..d6201010 100644
--- a/src/browser/webapi/element/Html.zig
+++ b/src/browser/webapi/element/Html.zig
@@ -410,7 +410,7 @@ pub fn hasAttributeFunction(self: *HtmlElement, listener_type: GlobalEventHandle
 fn setAttributeListener(
     self: *Element.Html,
     listener_type: GlobalEventHandler,
-    listener_callback: js.Function.Global,
+    listener_callback: ?js.Function.Global,
     page: *Page,
 ) !void {
     if (comptime IS_DEBUG) {
@@ -420,13 +420,22 @@ fn setAttributeListener(
         });
     }
 
-    try page._element_attr_listeners.put(page.arena, .{
+    if (listener_callback) |cb| {
+        try page._element_attr_listeners.put(page.arena, .{
+            .target = self.asEventTarget(),
+            .handler = listener_type,
+        }, cb);
+        return;
+    }
+
+    // The listener is null, remove existing listener.
+    _ = page._element_attr_listeners.remove(.{
         .target = self.asEventTarget(),
         .handler = listener_type,
-    }, listener_callback);
+    });
 }
 
-pub fn setOnAbort(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnAbort(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onabort, callback, page);
 }
 
@@ -434,7 +443,7 @@ pub fn getOnAbort(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onabort, page);
 }
 
-pub fn setOnAnimationCancel(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnAnimationCancel(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onanimationcancel, callback, page);
 }
 
@@ -442,7 +451,7 @@ pub fn getOnAnimationCancel(self: *HtmlElement, page: *Page) !?js.Function.Globa
     return self.getAttributeFunction(.onanimationcancel, page);
 }
 
-pub fn setOnAnimationEnd(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnAnimationEnd(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onanimationend, callback, page);
 }
 
@@ -450,7 +459,7 @@ pub fn getOnAnimationEnd(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onanimationend, page);
 }
 
-pub fn setOnAnimationIteration(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnAnimationIteration(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onanimationiteration, callback, page);
 }
 
@@ -458,7 +467,7 @@ pub fn getOnAnimationIteration(self: *HtmlElement, page: *Page) !?js.Function.Gl
     return self.getAttributeFunction(.onanimationiteration, page);
 }
 
-pub fn setOnAnimationStart(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnAnimationStart(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onanimationstart, callback, page);
 }
 
@@ -466,7 +475,7 @@ pub fn getOnAnimationStart(self: *HtmlElement, page: *Page) !?js.Function.Global
     return self.getAttributeFunction(.onanimationstart, page);
 }
 
-pub fn setOnAuxClick(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnAuxClick(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onauxclick, callback, page);
 }
 
@@ -474,7 +483,7 @@ pub fn getOnAuxClick(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onauxclick, page);
 }
 
-pub fn setOnBeforeInput(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnBeforeInput(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onbeforeinput, callback, page);
 }
 
@@ -482,7 +491,7 @@ pub fn getOnBeforeInput(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onbeforeinput, page);
 }
 
-pub fn setOnBeforeMatch(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnBeforeMatch(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onbeforematch, callback, page);
 }
 
@@ -490,7 +499,7 @@ pub fn getOnBeforeMatch(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onbeforematch, page);
 }
 
-pub fn setOnBeforeToggle(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnBeforeToggle(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onbeforetoggle, callback, page);
 }
 
@@ -498,7 +507,7 @@ pub fn getOnBeforeToggle(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onbeforetoggle, page);
 }
 
-pub fn setOnBlur(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnBlur(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onblur, callback, page);
 }
 
@@ -506,7 +515,7 @@ pub fn getOnBlur(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onblur, page);
 }
 
-pub fn setOnCancel(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnCancel(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oncancel, callback, page);
 }
 
@@ -514,7 +523,7 @@ pub fn getOnCancel(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.oncancel, page);
 }
 
-pub fn setOnCanPlay(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnCanPlay(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oncanplay, callback, page);
 }
 
@@ -522,7 +531,7 @@ pub fn getOnCanPlay(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.oncanplay, page);
 }
 
-pub fn setOnCanPlayThrough(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnCanPlayThrough(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oncanplaythrough, callback, page);
 }
 
@@ -530,7 +539,7 @@ pub fn getOnCanPlayThrough(self: *HtmlElement, page: *Page) !?js.Function.Global
     return self.getAttributeFunction(.oncanplaythrough, page);
 }
 
-pub fn setOnChange(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnChange(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onchange, callback, page);
 }
 
@@ -538,7 +547,7 @@ pub fn getOnChange(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onchange, page);
 }
 
-pub fn setOnClick(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnClick(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onclick, callback, page);
 }
 
@@ -546,7 +555,7 @@ pub fn getOnClick(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onclick, page);
 }
 
-pub fn setOnClose(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnClose(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onclose, callback, page);
 }
 
@@ -554,7 +563,7 @@ pub fn getOnClose(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onclose, page);
 }
 
-pub fn setOnCommand(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnCommand(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oncommand, callback, page);
 }
 
@@ -562,7 +571,7 @@ pub fn getOnCommand(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.oncommand, page);
 }
 
-pub fn setOnContentVisibilityAutoStateChange(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnContentVisibilityAutoStateChange(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oncontentvisibilityautostatechange, callback, page);
 }
 
@@ -570,7 +579,7 @@ pub fn getOnContentVisibilityAutoStateChange(self: *HtmlElement, page: *Page) !?
     return self.getAttributeFunction(.oncontentvisibilityautostatechange, page);
 }
 
-pub fn setOnContextLost(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnContextLost(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oncontextlost, callback, page);
 }
 
@@ -578,7 +587,7 @@ pub fn getOnContextLost(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.oncontextlost, page);
 }
 
-pub fn setOnContextMenu(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnContextMenu(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oncontextmenu, callback, page);
 }
 
@@ -586,7 +595,7 @@ pub fn getOnContextMenu(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.oncontextmenu, page);
 }
 
-pub fn setOnContextRestored(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnContextRestored(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oncontextrestored, callback, page);
 }
 
@@ -594,7 +603,7 @@ pub fn getOnContextRestored(self: *HtmlElement, page: *Page) !?js.Function.Globa
     return self.getAttributeFunction(.oncontextrestored, page);
 }
 
-pub fn setOnCopy(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnCopy(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oncopy, callback, page);
 }
 
@@ -602,7 +611,7 @@ pub fn getOnCopy(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.oncopy, page);
 }
 
-pub fn setOnCueChange(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnCueChange(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oncuechange, callback, page);
 }
 
@@ -610,7 +619,7 @@ pub fn getOnCueChange(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.oncuechange, page);
 }
 
-pub fn setOnCut(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnCut(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oncut, callback, page);
 }
 
@@ -618,7 +627,7 @@ pub fn getOnCut(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.oncut, page);
 }
 
-pub fn setOnDblClick(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnDblClick(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ondblclick, callback, page);
 }
 
@@ -626,7 +635,7 @@ pub fn getOnDblClick(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.ondblclick, page);
 }
 
-pub fn setOnDrag(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnDrag(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ondrag, callback, page);
 }
 
@@ -634,7 +643,7 @@ pub fn getOnDrag(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.ondrag, page);
 }
 
-pub fn setOnDragEnd(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnDragEnd(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ondragend, callback, page);
 }
 
@@ -642,7 +651,7 @@ pub fn getOnDragEnd(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.ondragend, page);
 }
 
-pub fn setOnDragEnter(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnDragEnter(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ondragenter, callback, page);
 }
 
@@ -650,7 +659,7 @@ pub fn getOnDragEnter(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.ondragenter, page);
 }
 
-pub fn setOnDragExit(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnDragExit(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ondragexit, callback, page);
 }
 
@@ -658,7 +667,7 @@ pub fn getOnDragExit(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.ondragexit, page);
 }
 
-pub fn setOnDragLeave(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnDragLeave(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ondragleave, callback, page);
 }
 
@@ -666,7 +675,7 @@ pub fn getOnDragLeave(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.ondragleave, page);
 }
 
-pub fn setOnDragOver(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnDragOver(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ondragover, callback, page);
 }
 
@@ -674,7 +683,7 @@ pub fn getOnDragOver(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.ondragover, page);
 }
 
-pub fn setOnDragStart(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnDragStart(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ondragstart, callback, page);
 }
 
@@ -682,7 +691,7 @@ pub fn getOnDragStart(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.ondragstart, page);
 }
 
-pub fn setOnDrop(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnDrop(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ondrop, callback, page);
 }
 
@@ -690,7 +699,7 @@ pub fn getOnDrop(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.ondrop, page);
 }
 
-pub fn setOnDurationChange(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnDurationChange(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ondurationchange, callback, page);
 }
 
@@ -698,7 +707,7 @@ pub fn getOnDurationChange(self: *HtmlElement, page: *Page) !?js.Function.Global
     return self.getAttributeFunction(.ondurationchange, page);
 }
 
-pub fn setOnEmptied(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnEmptied(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onemptied, callback, page);
 }
 
@@ -706,7 +715,7 @@ pub fn getOnEmptied(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onemptied, page);
 }
 
-pub fn setOnEnded(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnEnded(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onended, callback, page);
 }
 
@@ -714,7 +723,7 @@ pub fn getOnEnded(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onended, page);
 }
 
-pub fn setOnError(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnError(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onerror, callback, page);
 }
 
@@ -722,7 +731,7 @@ pub fn getOnError(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onerror, page);
 }
 
-pub fn setOnFocus(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnFocus(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onfocus, callback, page);
 }
 
@@ -730,7 +739,7 @@ pub fn getOnFocus(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onfocus, page);
 }
 
-pub fn setOnFormData(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnFormData(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onformdata, callback, page);
 }
 
@@ -738,7 +747,7 @@ pub fn getOnFormData(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onformdata, page);
 }
 
-pub fn setOnFullscreenChange(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnFullscreenChange(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onfullscreenchange, callback, page);
 }
 
@@ -746,7 +755,7 @@ pub fn getOnFullscreenChange(self: *HtmlElement, page: *Page) !?js.Function.Glob
     return self.getAttributeFunction(.onfullscreenchange, page);
 }
 
-pub fn setOnFullscreenError(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnFullscreenError(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onfullscreenerror, callback, page);
 }
 
@@ -754,7 +763,7 @@ pub fn getOnFullscreenError(self: *HtmlElement, page: *Page) !?js.Function.Globa
     return self.getAttributeFunction(.onfullscreenerror, page);
 }
 
-pub fn setOnGotPointerCapture(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnGotPointerCapture(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ongotpointercapture, callback, page);
 }
 
@@ -762,7 +771,7 @@ pub fn getOnGotPointerCapture(self: *HtmlElement, page: *Page) !?js.Function.Glo
     return self.getAttributeFunction(.ongotpointercapture, page);
 }
 
-pub fn setOnInput(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnInput(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oninput, callback, page);
 }
 
@@ -770,7 +779,7 @@ pub fn getOnInput(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.oninput, page);
 }
 
-pub fn setOnInvalid(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnInvalid(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.oninvalid, callback, page);
 }
 
@@ -778,7 +787,7 @@ pub fn getOnInvalid(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.oninvalid, page);
 }
 
-pub fn setOnKeyDown(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnKeyDown(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onkeydown, callback, page);
 }
 
@@ -786,7 +795,7 @@ pub fn getOnKeyDown(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onkeydown, page);
 }
 
-pub fn setOnKeyPress(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnKeyPress(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onkeypress, callback, page);
 }
 
@@ -794,7 +803,7 @@ pub fn getOnKeyPress(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onkeypress, page);
 }
 
-pub fn setOnKeyUp(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnKeyUp(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onkeyup, callback, page);
 }
 
@@ -802,7 +811,7 @@ pub fn getOnKeyUp(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onkeyup, page);
 }
 
-pub fn setOnLoad(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnLoad(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onload, callback, page);
 }
 
@@ -810,7 +819,7 @@ pub fn getOnLoad(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onload, page);
 }
 
-pub fn setOnLoadedData(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnLoadedData(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onloadeddata, callback, page);
 }
 
@@ -818,7 +827,7 @@ pub fn getOnLoadedData(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onloadeddata, page);
 }
 
-pub fn setOnLoadedMetadata(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnLoadedMetadata(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onloadedmetadata, callback, page);
 }
 
@@ -826,7 +835,7 @@ pub fn getOnLoadedMetadata(self: *HtmlElement, page: *Page) !?js.Function.Global
     return self.getAttributeFunction(.onloadedmetadata, page);
 }
 
-pub fn setOnLoadStart(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnLoadStart(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onloadstart, callback, page);
 }
 
@@ -834,7 +843,7 @@ pub fn getOnLoadStart(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onloadstart, page);
 }
 
-pub fn setOnLostPointerCapture(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnLostPointerCapture(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onlostpointercapture, callback, page);
 }
 
@@ -842,7 +851,7 @@ pub fn getOnLostPointerCapture(self: *HtmlElement, page: *Page) !?js.Function.Gl
     return self.getAttributeFunction(.onlostpointercapture, page);
 }
 
-pub fn setOnMouseDown(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnMouseDown(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onmousedown, callback, page);
 }
 
@@ -850,7 +859,7 @@ pub fn getOnMouseDown(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onmousedown, page);
 }
 
-pub fn setOnMouseMove(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnMouseMove(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onmousemove, callback, page);
 }
 
@@ -858,7 +867,7 @@ pub fn getOnMouseMove(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onmousemove, page);
 }
 
-pub fn setOnMouseOut(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnMouseOut(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onmouseout, callback, page);
 }
 
@@ -866,7 +875,7 @@ pub fn getOnMouseOut(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onmouseout, page);
 }
 
-pub fn setOnMouseOver(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnMouseOver(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onmouseover, callback, page);
 }
 
@@ -874,7 +883,7 @@ pub fn getOnMouseOver(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onmouseover, page);
 }
 
-pub fn setOnMouseUp(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnMouseUp(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onmouseup, callback, page);
 }
 
@@ -882,7 +891,7 @@ pub fn getOnMouseUp(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onmouseup, page);
 }
 
-pub fn setOnPaste(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPaste(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onpaste, callback, page);
 }
 
@@ -890,7 +899,7 @@ pub fn getOnPaste(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onpaste, page);
 }
 
-pub fn setOnPause(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPause(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onpause, callback, page);
 }
 
@@ -898,7 +907,7 @@ pub fn getOnPause(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onpause, page);
 }
 
-pub fn setOnPlay(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPlay(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onplay, callback, page);
 }
 
@@ -906,7 +915,7 @@ pub fn getOnPlay(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onplay, page);
 }
 
-pub fn setOnPlaying(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPlaying(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onplaying, callback, page);
 }
 
@@ -914,7 +923,7 @@ pub fn getOnPlaying(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onplaying, page);
 }
 
-pub fn setOnPointerCancel(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPointerCancel(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onpointercancel, callback, page);
 }
 
@@ -922,7 +931,7 @@ pub fn getOnPointerCancel(self: *HtmlElement, page: *Page) !?js.Function.Global
     return self.getAttributeFunction(.onpointercancel, page);
 }
 
-pub fn setOnPointerDown(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPointerDown(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onpointerdown, callback, page);
 }
 
@@ -930,7 +939,7 @@ pub fn getOnPointerDown(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onpointerdown, page);
 }
 
-pub fn setOnPointerEnter(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPointerEnter(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onpointerenter, callback, page);
 }
 
@@ -938,7 +947,7 @@ pub fn getOnPointerEnter(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onpointerenter, page);
 }
 
-pub fn setOnPointerLeave(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPointerLeave(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onpointerleave, callback, page);
 }
 
@@ -946,7 +955,7 @@ pub fn getOnPointerLeave(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onpointerleave, page);
 }
 
-pub fn setOnPointerMove(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPointerMove(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onpointermove, callback, page);
 }
 
@@ -954,7 +963,7 @@ pub fn getOnPointerMove(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onpointermove, page);
 }
 
-pub fn setOnPointerOut(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPointerOut(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onpointerout, callback, page);
 }
 
@@ -962,7 +971,7 @@ pub fn getOnPointerOut(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onpointerout, page);
 }
 
-pub fn setOnPointerOver(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPointerOver(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onpointerover, callback, page);
 }
 
@@ -970,7 +979,7 @@ pub fn getOnPointerOver(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onpointerover, page);
 }
 
-pub fn setOnPointerRawUpdate(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPointerRawUpdate(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onpointerrawupdate, callback, page);
 }
 
@@ -978,7 +987,7 @@ pub fn getOnPointerRawUpdate(self: *HtmlElement, page: *Page) !?js.Function.Glob
     return self.getAttributeFunction(.onpointerrawupdate, page);
 }
 
-pub fn setOnPointerUp(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnPointerUp(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onpointerup, callback, page);
 }
 
@@ -986,7 +995,7 @@ pub fn getOnPointerUp(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onpointerup, page);
 }
 
-pub fn setOnProgress(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnProgress(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onprogress, callback, page);
 }
 
@@ -994,7 +1003,7 @@ pub fn getOnProgress(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onprogress, page);
 }
 
-pub fn setOnRateChange(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnRateChange(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onratechange, callback, page);
 }
 
@@ -1002,7 +1011,7 @@ pub fn getOnRateChange(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onratechange, page);
 }
 
-pub fn setOnReset(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnReset(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onreset, callback, page);
 }
 
@@ -1010,7 +1019,7 @@ pub fn getOnReset(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onreset, page);
 }
 
-pub fn setOnResize(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnResize(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onresize, callback, page);
 }
 
@@ -1018,7 +1027,7 @@ pub fn getOnResize(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onresize, page);
 }
 
-pub fn setOnScroll(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnScroll(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onscroll, callback, page);
 }
 
@@ -1026,7 +1035,7 @@ pub fn getOnScroll(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onscroll, page);
 }
 
-pub fn setOnScrollEnd(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnScrollEnd(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onscrollend, callback, page);
 }
 
@@ -1034,7 +1043,7 @@ pub fn getOnScrollEnd(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onscrollend, page);
 }
 
-pub fn setOnSecurityPolicyViolation(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnSecurityPolicyViolation(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onsecuritypolicyviolation, callback, page);
 }
 
@@ -1042,7 +1051,7 @@ pub fn getOnSecurityPolicyViolation(self: *HtmlElement, page: *Page) !?js.Functi
     return self.getAttributeFunction(.onsecuritypolicyviolation, page);
 }
 
-pub fn setOnSeeked(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnSeeked(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onseeked, callback, page);
 }
 
@@ -1050,7 +1059,7 @@ pub fn getOnSeeked(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onseeked, page);
 }
 
-pub fn setOnSeeking(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnSeeking(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onseeking, callback, page);
 }
 
@@ -1058,7 +1067,7 @@ pub fn getOnSeeking(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onseeking, page);
 }
 
-pub fn setOnSelect(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnSelect(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onselect, callback, page);
 }
 
@@ -1066,7 +1075,7 @@ pub fn getOnSelect(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onselect, page);
 }
 
-pub fn setOnSelectionChange(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnSelectionChange(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onselectionchange, callback, page);
 }
 
@@ -1074,7 +1083,7 @@ pub fn getOnSelectionChange(self: *HtmlElement, page: *Page) !?js.Function.Globa
     return self.getAttributeFunction(.onselectionchange, page);
 }
 
-pub fn setOnSelectStart(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnSelectStart(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onselectstart, callback, page);
 }
 
@@ -1082,7 +1091,7 @@ pub fn getOnSelectStart(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onselectstart, page);
 }
 
-pub fn setOnSlotChange(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnSlotChange(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onslotchange, callback, page);
 }
 
@@ -1090,7 +1099,7 @@ pub fn getOnSlotChange(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onslotchange, page);
 }
 
-pub fn setOnStalled(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnStalled(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onstalled, callback, page);
 }
 
@@ -1098,7 +1107,7 @@ pub fn getOnStalled(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onstalled, page);
 }
 
-pub fn setOnSubmit(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnSubmit(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onsubmit, callback, page);
 }
 
@@ -1106,7 +1115,7 @@ pub fn getOnSubmit(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onsubmit, page);
 }
 
-pub fn setOnSuspend(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnSuspend(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onsuspend, callback, page);
 }
 
@@ -1114,7 +1123,7 @@ pub fn getOnSuspend(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onsuspend, page);
 }
 
-pub fn setOnTimeUpdate(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnTimeUpdate(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ontimeupdate, callback, page);
 }
 
@@ -1122,7 +1131,7 @@ pub fn getOnTimeUpdate(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.ontimeupdate, page);
 }
 
-pub fn setOnToggle(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnToggle(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ontoggle, callback, page);
 }
 
@@ -1130,7 +1139,7 @@ pub fn getOnToggle(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.ontoggle, page);
 }
 
-pub fn setOnTransitionCancel(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnTransitionCancel(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ontransitioncancel, callback, page);
 }
 
@@ -1138,7 +1147,7 @@ pub fn getOnTransitionCancel(self: *HtmlElement, page: *Page) !?js.Function.Glob
     return self.getAttributeFunction(.ontransitioncancel, page);
 }
 
-pub fn setOnTransitionEnd(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnTransitionEnd(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ontransitionend, callback, page);
 }
 
@@ -1146,7 +1155,7 @@ pub fn getOnTransitionEnd(self: *HtmlElement, page: *Page) !?js.Function.Global
     return self.getAttributeFunction(.ontransitionend, page);
 }
 
-pub fn setOnTransitionRun(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnTransitionRun(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ontransitionrun, callback, page);
 }
 
@@ -1154,7 +1163,7 @@ pub fn getOnTransitionRun(self: *HtmlElement, page: *Page) !?js.Function.Global
     return self.getAttributeFunction(.ontransitionrun, page);
 }
 
-pub fn setOnTransitionStart(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnTransitionStart(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.ontransitionstart, callback, page);
 }
 
@@ -1162,7 +1171,7 @@ pub fn getOnTransitionStart(self: *HtmlElement, page: *Page) !?js.Function.Globa
     return self.getAttributeFunction(.ontransitionstart, page);
 }
 
-pub fn setOnVolumeChange(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnVolumeChange(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onvolumechange, callback, page);
 }
 
@@ -1170,7 +1179,7 @@ pub fn getOnVolumeChange(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onvolumechange, page);
 }
 
-pub fn setOnWaiting(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnWaiting(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onwaiting, callback, page);
 }
 
@@ -1178,7 +1187,7 @@ pub fn getOnWaiting(self: *HtmlElement, page: *Page) !?js.Function.Global {
     return self.getAttributeFunction(.onwaiting, page);
 }
 
-pub fn setOnWheel(self: *HtmlElement, callback: js.Function.Global, page: *Page) !void {
+pub fn setOnWheel(self: *HtmlElement, callback: ?js.Function.Global, page: *Page) !void {
     return self.setAttributeListener(.onwheel, callback, page);
 }