diff --git a/src/browser/js/bridge.zig b/src/browser/js/bridge.zig
index d6c4f12b6..0fae5bd58 100644
--- a/src/browser/js/bridge.zig
+++ b/src/browser/js/bridge.zig
@@ -300,6 +300,8 @@ pub const Indexed = struct {
     const Opts = struct {
         as_typed_array: bool = false,
         null_as_undefined: bool = false,
+        // Only applies to setter and deleter; getters don't mutate.
+        ce_reactions: bool = false,
     };
 
     fn init(comptime T: type, comptime getter: anytype, setter: anytype, deleter: anytype, query: anytype, definer: anytype, comptime enumerator: anytype, comptime opts: Opts) Indexed {
@@ -346,6 +348,18 @@ pub const Indexed = struct {
                     }
                     defer caller.deinit();
 
+                    const ce_frame: ?*Frame = if (comptime opts.ce_reactions) switch (caller.local.ctx.global) {
+                        .frame => |frame| frame,
+                        .worker => null,
+                    } else null;
+                    var ce_checkpoint: usize = undefined;
+                    if (comptime opts.ce_reactions) {
+                        if (ce_frame) |frame| ce_checkpoint = frame._ce_reactions.push();
+                    }
+                    defer if (comptime opts.ce_reactions) {
+                        if (ce_frame) |frame| frame._ce_reactions.popAndInvoke(ce_checkpoint, frame);
+                    };
+
                     return caller.setIndex(T, setter, idx, c_value.?, handle.?, .{
                         .as_typed_array = opts.as_typed_array,
                         .null_as_undefined = opts.null_as_undefined,
@@ -364,6 +378,18 @@ pub const Indexed = struct {
                     }
                     defer caller.deinit();
 
+                    const ce_frame: ?*Frame = if (comptime opts.ce_reactions) switch (caller.local.ctx.global) {
+                        .frame => |frame| frame,
+                        .worker => null,
+                    } else null;
+                    var ce_checkpoint: usize = undefined;
+                    if (comptime opts.ce_reactions) {
+                        if (ce_frame) |frame| ce_checkpoint = frame._ce_reactions.push();
+                    }
+                    defer if (comptime opts.ce_reactions) {
+                        if (ce_frame) |frame| frame._ce_reactions.popAndInvoke(ce_checkpoint, frame);
+                    };
+
                     return caller.deleteOrDefineIndex(T, deleter, idx, handle.?, .{
                         .as_typed_array = opts.as_typed_array,
                         .null_as_undefined = opts.null_as_undefined,
diff --git a/src/browser/tests/collections/html_all_collection.html b/src/browser/tests/collections/html_all_collection.html
index 62bb4138c..87993069f 100644
--- a/src/browser/tests/collections/html_all_collection.html
+++ b/src/browser/tests/collections/html_all_collection.html
@@ -103,3 +103,25 @@
     testing.expectEqual(false, !!document.all);
   }
 </script>
+
+<script id=all_named_presence>
+  {
+    const all = document.all;
+
+    testing.expectEqual(true, 'a' in all);
+    testing.expectEqual(true, 'field' in all);
+    testing.expectEqual(true, 'anchor' in all);
+    testing.expectEqual(true, Object.hasOwn(all, 'b'));
+
+    testing.expectEqual(false, 'nonExistent' in all);
+    testing.expectEqual(false, Object.hasOwn(all, 'nonExistent'));
+
+    // name= only counts for the elements document.all exposes by name,
+    // so a named div is reachable by id but not by name
+    testing.expectEqual(false, 'alpha' in all);
+
+    // [LegacyUnenumerableNamedProperties]
+    testing.expectEqual(false, Object.keys(all).includes('a'));
+    testing.expectEqual(false, Object.getOwnPropertyDescriptor(all, 'a').enumerable);
+  }
+</script>
diff --git a/src/browser/tests/element/attributes.html b/src/browser/tests/element/attributes.html
index 68652e5ef..384f3e489 100644
--- a/src/browser/tests/element/attributes.html
+++ b/src/browser/tests/element/attributes.html
@@ -2,6 +2,7 @@
 <script src="../testing.js"></script>
 
 <div id=attr1 ClasS="sHow"></div>
+<div id=nnm class=box data-role=widget></div>
 
 <script id=attributes>
   const el1 = $('#attr1');
@@ -319,3 +320,44 @@
     testing.expectEqual('s', el.getAttribute('slot'));
   }
 </script>
+
+<script id=named_node_map_presence>
+{
+  const attrs = $('#nnm').attributes;
+
+  testing.expectEqual(true, 'id' in attrs);
+  testing.expectEqual(true, 'data-role' in attrs);
+  testing.expectEqual(true, Object.hasOwn(attrs, 'class'));
+
+  testing.expectEqual(false, 'nonExistent' in attrs);
+  testing.expectEqual(false, Object.hasOwn(attrs, 'nonExistent'));
+
+  // presence tracks the attribute list
+  $('#nnm').setAttribute('title', 'hi');
+  testing.expectEqual(true, 'title' in attrs);
+  $('#nnm').removeAttribute('title');
+  testing.expectEqual(false, 'title' in attrs);
+
+  // inherited members are found by `in`, but are not own properties
+  testing.expectEqual(true, 'length' in attrs);
+  testing.expectEqual(false, Object.hasOwn(attrs, 'length'));
+}
+</script>
+
+<script id=named_node_map_enumeration>
+{
+  const attrs = $('#nnm').attributes;
+
+  // [LegacyUnenumerableNamedProperties]: only the indices enumerate...
+  testing.expectEqual('0,1,2', Object.keys(attrs).join(','));
+
+  // ...but the names are still own properties
+  const own = Object.getOwnPropertyNames(attrs);
+  testing.expectEqual(true, own.includes('id'));
+  testing.expectEqual(true, own.includes('class'));
+  testing.expectEqual(true, own.includes('data-role'));
+
+  testing.expectEqual(false, Object.getOwnPropertyDescriptor(attrs, 'id').enumerable);
+  testing.expectEqual('id', Object.getOwnPropertyDescriptor(attrs, 'id').value.name);
+}
+</script>
diff --git a/src/browser/tests/element/dataset.html b/src/browser/tests/element/dataset.html
index 3df34585b..552e4af1f 100644
--- a/src/browser/tests/element/dataset.html
+++ b/src/browser/tests/element/dataset.html
@@ -121,6 +121,104 @@
 }
 </script>
 
+<script id=propertyEnumeration>
+{
+  const el = document.getElementById('test');
+
+  // dataset is not [LegacyUnenumerableNamedProperties]: the names enumerate.
+  testing.expectEqual('foo,helloWorld', Object.keys(el.dataset).join(','));
+  testing.expectEqual('foo,helloWorld', Object.getOwnPropertyNames(el.dataset).join(','));
+  testing.expectEqual('{"foo":"bar","helloWorld":"test"}', JSON.stringify(el.dataset));
+
+  const desc = Object.getOwnPropertyDescriptor(el.dataset, 'foo');
+  testing.expectEqual('bar', desc.value);
+  testing.expectEqual(true, desc.enumerable);
+  testing.expectEqual(true, desc.configurable);
+  testing.expectEqual(true, desc.writable);
+  testing.expectEqual(undefined, Object.getOwnPropertyDescriptor(el.dataset, 'nonExistent'));
+
+  // inherited properties are still found by `in`, but are not own
+  testing.expectEqual(true, 'toString' in el.dataset);
+  testing.expectEqual(false, Object.hasOwn(el.dataset, 'toString'));
+}
+</script>
+
+<script id=presenceTracksAttribute>
+{
+  const el = document.createElement('div');
+  const ds = el.dataset;
+
+  testing.expectEqual(false, 'live' in ds);
+  el.setAttribute('data-live', 'x');
+  testing.expectEqual(true, 'live' in ds);
+  el.removeAttribute('data-live');
+  testing.expectEqual(false, 'live' in ds);
+
+  ds.viaSetter = 'y';
+  testing.expectEqual(true, 'viaSetter' in ds);
+  delete ds.viaSetter;
+  testing.expectEqual(false, 'viaSetter' in ds);
+
+  // an empty value is still a present property
+  el.setAttribute('data-empty', '');
+  testing.expectEqual(true, 'empty' in ds);
+  testing.expectEqual('', ds.empty);
+
+  // the bare data- attribute maps to the empty name
+  el.setAttribute('data-', 'bare');
+  testing.expectEqual(true, '' in ds);
+  testing.expectEqual('bare', ds['']);
+
+  // deleting a name that was never there succeeds
+  testing.expectEqual(true, delete ds.neverThere);
+}
+</script>
+
+<script id=numericPropertyNames>
+{
+  const el = document.createElement('div');
+
+  el.dataset[0] = 'zero';
+  testing.expectEqual('zero', el.getAttribute('data-0'));
+  testing.expectEqual('zero', el.dataset[0]);
+  testing.expectEqual('zero', el.dataset['0']);
+  testing.expectEqual(true, '0' in el.dataset);
+  testing.expectEqual(true, Object.hasOwn(el.dataset, '0'));
+  testing.expectEqual('0', Object.keys(el.dataset).join(','));
+
+  delete el.dataset[0];
+  testing.expectEqual(null, el.getAttribute('data-0'));
+  testing.expectEqual(undefined, el.dataset[0]);
+  testing.expectEqual(false, '0' in el.dataset);
+
+  el.setAttribute('data-12', 'twelve');
+  testing.expectEqual('twelve', el.dataset[12]);
+  testing.expectEqual('twelve', el.dataset['12']);
+  testing.expectEqual(true, '12' in el.dataset);
+  testing.expectEqual(false, '13' in el.dataset);
+}
+</script>
+
+<script id=indexedSetRunsCustomElementReactions>
+{
+  const seen = [];
+  class DataWatcher extends HTMLElement {
+    static get observedAttributes() { return ['data-0', 'data-name']; }
+    attributeChangedCallback(name, oldValue, newValue) {
+      seen.push(name + '=' + newValue);
+    }
+  }
+  customElements.define('data-watcher', DataWatcher);
+
+  const el = document.createElement('data-watcher');
+  el.dataset.name = 'named';
+  el.dataset[0] = 'indexed';
+  delete el.dataset[0];
+
+  testing.expectEqual('data-name=named,data-0=indexed,data-0=null', seen.join(','));
+}
+</script>
+
 <script id=identityCheck>
 {
   const el = document.getElementById('test');
diff --git a/src/browser/tests/element/html/form.html b/src/browser/tests/element/html/form.html
index b8c1cdb87..2612be61c 100644
--- a/src/browser/tests/element/html/form.html
+++ b/src/browser/tests/element/html/form.html
@@ -5,6 +5,13 @@
 <form id="form_with_name" name="myForm"></form>
 <form id="form_without_name"></form>
 
+<form id="form_controls">
+  <input name="user" autocomplete="off">
+  <input id="pass" type="password" autocomplete="off">
+  <input type="radio" name="choice" value="1" autocomplete="off">
+  <input type="radio" name="choice" value="2" autocomplete="off">
+</form>
+
 <script id="name_initial">
 {
   testing.expectEqual('myForm', $('#form_with_name').name)
@@ -661,3 +668,24 @@
   testing.expectEqual('InvalidStateError', caught);
 }
 </script>
+
+<script id="elements_named_presence">
+{
+  const els = $('#form_controls').elements;
+
+  testing.expectEqual(true, 'user' in els);
+  testing.expectEqual(true, 'pass' in els);
+  testing.expectEqual(true, Object.hasOwn(els, 'choice'));
+
+  testing.expectEqual(false, 'nonExistent' in els);
+  testing.expectEqual(false, Object.hasOwn(els, 'nonExistent'));
+  testing.expectEqual(false, '' in els);
+
+  // a duplicated name is still one present property, backed by a RadioNodeList
+  testing.expectEqual('RadioNodeList', els.choice.constructor.name);
+
+  // [LegacyUnenumerableNamedProperties]
+  testing.expectEqual(false, Object.keys(els).includes('user'));
+  testing.expectEqual(false, Object.getOwnPropertyDescriptor(els, 'user').enumerable);
+}
+</script>
diff --git a/src/browser/tests/element/html/select.html b/src/browser/tests/element/html/select.html
index 6d36c8b76..2de2b0dc5 100644
--- a/src/browser/tests/element/html/select.html
+++ b/src/browser/tests/element/html/select.html
@@ -7,6 +7,11 @@
   <option value="val3">Option 3</option>
 </select>
 
+<select id="select_named" autocomplete="off">
+  <option id="opt_first" value="1">First</option>
+  <option name="second" value="2">Second</option>
+</select>
+
 <select id="select2" autocomplete="off">
   <option value="a">A</option>
   <option value="b">B</option>
@@ -522,3 +527,20 @@
   testing.expectEqual(true, orphan.selected);
 }
 </script>
+
+<script id="options_named_presence">
+{
+  const opts = $('#select_named').options;
+
+  testing.expectEqual(true, 'opt_first' in opts);
+  testing.expectEqual(true, 'second' in opts);
+  testing.expectEqual(true, Object.hasOwn(opts, 'opt_first'));
+
+  testing.expectEqual(false, 'nonExistent' in opts);
+  testing.expectEqual(false, Object.hasOwn(opts, 'nonExistent'));
+
+  // [LegacyUnenumerableNamedProperties]
+  testing.expectEqual(false, Object.keys(opts).includes('opt_first'));
+  testing.expectEqual(false, Object.getOwnPropertyDescriptor(opts, 'opt_first').enumerable);
+}
+</script>
diff --git a/src/browser/tests/navigator/navigator.html b/src/browser/tests/navigator/navigator.html
index 96fc09014..78156be4e 100644
--- a/src/browser/tests/navigator/navigator.html
+++ b/src/browser/tests/navigator/navigator.html
@@ -51,6 +51,16 @@
   }
 </script>
 
+<script id=navigator_plugins_named_presence>
+  // No plugin is exposed, so PluginArray has no named properties at all.
+  testing.expectEqual(false, 'anything' in navigator.plugins);
+  testing.expectEqual(false, Object.hasOwn(navigator.plugins, 'anything'));
+  testing.expectEqual(null, navigator.plugins.namedItem('anything'));
+
+  // inherited members are still found by `in`
+  testing.expectEqual(true, 'refresh' in navigator.plugins);
+</script>
+
 <script id=navigator_plugins_iterable>
   // WebIDL: indexed getter => @@iterator (Chrome: [...navigator.plugins] works)
   testing.expectEqual('function', typeof navigator.plugins[Symbol.iterator]);
diff --git a/src/browser/webapi/PluginArray.zig b/src/browser/webapi/PluginArray.zig
index 31fffe286..3f0fe69d5 100644
--- a/src/browser/webapi/PluginArray.zig
+++ b/src/browser/webapi/PluginArray.zig
@@ -78,14 +78,22 @@ pub const JsApi = struct {
     pub const length = bridge.property(0, .{ .template = false });
     pub const refresh = bridge.function(PluginArray.refresh, .{});
     pub const @"[int]" = bridge.indexed(PluginArray.getAtIndex, null, .{ .null_as_undefined = true });
-    pub const @"[str]" = bridge.namedIndexed(PluginArray.getByName, null, null, null, null, .{ .null_as_undefined = true });
-    pub const item = bridge.function(_item, .{});
-    fn _item(self: *const PluginArray, index: i32) ?*Plugin {
-        if (index < 0) {
-            return null;
+    pub const @"[str]" = bridge.namedIndexed(PluginArray.getByName, null, null, null, struct {
+        fn wrap(_: *const PluginArray, _: []const u8) !u32 {
+            // No plugin is ever exposed, so there are no named properties.
+            return error.NotHandled;
         }
-        return self.getAtIndex(@intCast(index));
-    }
+    }.wrap, .{ .null_as_undefined = true });
+
+    pub const item = bridge.function(struct {
+        fn wrap(self: *const PluginArray, index: i32) ?*Plugin {
+            if (index < 0) {
+                return null;
+            }
+            return self.getAtIndex(@intCast(index));
+        }
+    }.wrap, .{});
+
     pub const namedItem = bridge.function(PluginArray.getByName, .{});
     pub const symbol_iterator = bridge.iterator(PluginArray.values, .{});
 };
diff --git a/src/browser/webapi/collections/HTMLAllCollection.zig b/src/browser/webapi/collections/HTMLAllCollection.zig
index 42c38999c..03e0cb757 100644
--- a/src/browser/webapi/collections/HTMLAllCollection.zig
+++ b/src/browser/webapi/collections/HTMLAllCollection.zig
@@ -125,15 +125,24 @@ pub const JsApi = struct {
 
     pub const length = bridge.accessor(HTMLAllCollection.length, null, .{});
     pub const @"[int]" = bridge.indexed(HTMLAllCollection.getAtIndex, null, .{ .null_as_undefined = true });
-    pub const @"[str]" = bridge.namedIndexed(HTMLAllCollection.getByName, null, null, null, null, .{ .null_as_undefined = true });
-
-    pub const item = bridge.function(_item, .{});
-    fn _item(self: *HTMLAllCollection, index: i32, frame: *Frame) ?*Element {
-        if (index < 0) {
-            return null;
+    pub const @"[str]" = bridge.namedIndexed(HTMLAllCollection.getByName, null, null, null, struct {
+        fn wrap(self: *HTMLAllCollection, name: []const u8, frame: *Frame) !u32 {
+            if (self.getByName(name, frame) != null) {
+                // Named properties are [LegacyUnenumerableNamedProperties]
+                return js.v8.DontEnum;
+            }
+            return error.NotHandled;
         }
-        return self.getAtIndex(@intCast(index), frame);
-    }
+    }.wrap, .{ .null_as_undefined = true });
+
+    pub const item = bridge.function(struct {
+        fn wrap(self: *HTMLAllCollection, index: i32, frame: *Frame) ?*Element {
+            if (index < 0) {
+                return null;
+            }
+            return self.getAtIndex(@intCast(index), frame);
+        }
+    }.wrap, .{});
 
     pub const namedItem = bridge.function(HTMLAllCollection.getByName, .{});
     pub const symbol_iterator = bridge.iterator(HTMLAllCollection.iterator, .{});
diff --git a/src/browser/webapi/collections/HTMLFormControlsCollection.zig b/src/browser/webapi/collections/HTMLFormControlsCollection.zig
index a71070ad4..8e3300085 100644
--- a/src/browser/webapi/collections/HTMLFormControlsCollection.zig
+++ b/src/browser/webapi/collections/HTMLFormControlsCollection.zig
@@ -74,21 +74,7 @@ pub fn namedItem(self: *HTMLFormControlsCollection, name: []const u8, frame: *Fr
 
     var it = try self.iterator();
     while (it.next()) |element| {
-        const is_match = blk: {
-            if (element.getId()) |id| {
-                if (std.mem.eql(u8, id, name)) {
-                    break :blk true;
-                }
-            }
-            if (element.getName()) |elem_name| {
-                if (std.mem.eql(u8, elem_name, name)) {
-                    break :blk true;
-                }
-            }
-            break :blk false;
-        };
-
-        if (is_match) {
+        if (matchesName(element, name)) {
             if (first_element == null) {
                 first_element = element;
             }
@@ -126,6 +112,20 @@ pub fn namedItem(self: *HTMLFormControlsCollection, name: []const u8, frame: *Fr
     return .{ .element = first_element.? };
 }
 
+fn matchesName(element: *Element, name: []const u8) bool {
+    if (element.getId()) |id| {
+        if (std.mem.eql(u8, id, name)) {
+            return true;
+        }
+    }
+    if (element.getName()) |elem_name| {
+        if (std.mem.eql(u8, elem_name, name)) {
+            return true;
+        }
+    }
+    return false;
+}
+
 // used internally, by HTMLFormControlsCollection and RadioNodeList
 pub fn iterator(self: *HTMLFormControlsCollection) !Iterator {
     const form_collection = self._proto._data.form;
@@ -161,6 +161,30 @@ pub const JsApi = struct {
 
     pub const length = bridge.accessor(HTMLFormControlsCollection.length, null, .{});
     pub const @"[int]" = bridge.indexed(HTMLFormControlsCollection.getAtIndex, null, .{ .null_as_undefined = true });
-    pub const @"[str]" = bridge.namedIndexed(HTMLFormControlsCollection.namedItem, null, null, null, null, .{ .null_as_undefined = true });
+    pub const @"[str]" = bridge.namedIndexed(HTMLFormControlsCollection.namedItem, null, null, null, struct {
+        fn wrap(self: *HTMLFormControlsCollection, name: []const u8) !u32 {
+            if (try hasNamed(self, name)) {
+                // Named properties are [LegacyUnenumerableNamedProperties]
+                return js.v8.DontEnum;
+            }
+            return error.NotHandled;
+        }
+    }.wrap, .{ .null_as_undefined = true });
+
     pub const namedItem = bridge.function(HTMLFormControlsCollection.namedItem, .{});
+
+    // Presence only, `namedItem` is relativel expensive / RC'd
+    fn hasNamed(self: *HTMLFormControlsCollection, name: []const u8) !bool {
+        if (name.len == 0) {
+            return false;
+        }
+
+        var it = try self.iterator();
+        while (it.next()) |element| {
+            if (matchesName(element, name)) {
+                return true;
+            }
+        }
+        return false;
+    }
 };
diff --git a/src/browser/webapi/collections/HTMLOptionsCollection.zig b/src/browser/webapi/collections/HTMLOptionsCollection.zig
index 7a1f638ae..968405868 100644
--- a/src/browser/webapi/collections/HTMLOptionsCollection.zig
+++ b/src/browser/webapi/collections/HTMLOptionsCollection.zig
@@ -118,7 +118,15 @@ pub const JsApi = struct {
 
     // Indexed access
     pub const @"[int]" = bridge.indexed(HTMLOptionsCollection.getAtIndex, null, .{ .null_as_undefined = true });
-    pub const @"[str]" = bridge.namedIndexed(HTMLOptionsCollection.getByName, null, null, null, null, .{ .null_as_undefined = true });
+    pub const @"[str]" = bridge.namedIndexed(HTMLOptionsCollection.getByName, null, null, null, struct {
+        fn wrap(self: *HTMLOptionsCollection, name: []const u8, frame: *Frame) !u32 {
+            if (self.getByName(name, frame) != null) {
+                // Named properties are [LegacyUnenumerableNamedProperties]: the query
+                return js.v8.DontEnum;
+            }
+            return error.NotHandled;
+        }
+    }.wrap, .{ .null_as_undefined = true });
 
     pub const selectedIndex = bridge.accessor(HTMLOptionsCollection.getSelectedIndex, HTMLOptionsCollection.setSelectedIndex, .{});
     pub const add = bridge.function(HTMLOptionsCollection.add, .{ .ce_reactions = true });
diff --git a/src/browser/webapi/element/Attribute.zig b/src/browser/webapi/element/Attribute.zig
index e8766663f..f1ee47e60 100644
--- a/src/browser/webapi/element/Attribute.zig
+++ b/src/browser/webapi/element/Attribute.zig
@@ -661,26 +661,36 @@ pub const NamedNodeMap = struct {
         };
 
         pub const length = bridge.accessor(NamedNodeMap.length, null, .{});
-        pub const @"[int]" = bridge.indexed(NamedNodeMap.getAtIndex, getIndexes, .{ .null_as_undefined = true });
-        pub const @"[str]" = bridge.namedIndexed(NamedNodeMap.getByName, null, null, getNames, null, .{ .null_as_undefined = true });
-
-        fn getIndexes(self: *const NamedNodeMap, frame: *Frame) !js.Array {
-            const len = self.length();
-            var arr = frame.js.local.?.newArray(len);
-            for (0..len) |i| {
-                _ = try arr.set(@intCast(i), i, .{});
+        pub const @"[int]" = bridge.indexed(NamedNodeMap.getAtIndex, struct {
+            fn wrap(self: *const NamedNodeMap, frame: *Frame) !js.Array {
+                const len = self.length();
+                var arr = frame.js.local.?.newArray(len);
+                for (0..len) |i| {
+                    _ = try arr.set(@intCast(i), i, .{});
+                }
+                return arr;
             }
-            return arr;
-        }
+        }.wrap, .{ .null_as_undefined = true });
 
-        fn getNames(self: *const NamedNodeMap, frame: *Frame) !js.Array {
-            const names = try self.list().getNames(frame.local_arena);
-            var arr = frame.js.local.?.newArray(@intCast(names.len));
-            for (names, 0..) |name, i| {
-                _ = try arr.set(@intCast(i), name, .{});
+        pub const @"[str]" = bridge.namedIndexed(NamedNodeMap.getByName, null, null, struct {
+            fn wrap(self: *const NamedNodeMap, frame: *Frame) !js.Array {
+                const names = try self.list().getNames(frame.local_arena);
+                var arr = frame.js.local.?.newArray(@intCast(names.len));
+                for (names, 0..) |name, i| {
+                    _ = try arr.set(@intCast(i), name, .{});
+                }
+                return arr;
             }
-            return arr;
-        }
+        }.wrap, struct {
+            fn wrap(self: *const NamedNodeMap, name: String, frame: *Frame) !u32 {
+                if ((try self.list().get(name, frame)) != null) {
+                    // Named properties are [LegacyUnenumerableNamedProperties]
+                    return js.v8.DontEnum;
+                }
+                return error.NotHandled;
+            }
+        }.wrap, .{ .null_as_undefined = true });
+
         pub const getNamedItem = bridge.function(NamedNodeMap.getByName, .{});
         pub const setNamedItem = bridge.function(NamedNodeMap.set, .{ .ce_reactions = true });
         pub const removeNamedItem = bridge.function(NamedNodeMap.removeByName, .{ .ce_reactions = true });
diff --git a/src/browser/webapi/element/DOMStringMap.zig b/src/browser/webapi/element/DOMStringMap.zig
index dab5aaf41..9bdaedb8c 100644
--- a/src/browser/webapi/element/DOMStringMap.zig
+++ b/src/browser/webapi/element/DOMStringMap.zig
@@ -142,6 +142,30 @@ pub const JsApi = struct {
 
     pub const @"[]" = bridge.namedIndexed(getProperty, setProperty, deleteProperty, getNames, hasProperty, .{ .null_as_undefined = true, .ce_reactions = true });
 
+    // v8 routes dataset[9] and dataset["9"] to the indexed interceptor
+    pub const @"[int]" = bridge.indexedReadWrite(_getByIndex, _setByIndex, _deleteByIndex, _queryByIndex, null, .{ .null_as_undefined = true, .ce_reactions = true });
+
+    fn _getByIndex(self: *DOMStringMap, idx: u32, frame: *Frame) !?String {
+        return self._element.getAttribute(try indexName(idx, frame), frame);
+    }
+
+    fn _setByIndex(self: *DOMStringMap, idx: u32, value: String, frame: *Frame) !void {
+        return self._element.setAttributeSafe(try indexName(idx, frame), value, frame);
+    }
+
+    fn _deleteByIndex(self: *DOMStringMap, idx: u32, frame: *Frame) !void {
+        return self._element.removeAttribute(try indexName(idx, frame), frame);
+    }
+
+    fn _queryByIndex(self: *DOMStringMap, idx: u32, frame: *Frame) !bool {
+        return self._element.hasAttribute(try indexName(idx, frame), frame);
+    }
+    fn indexName(idx: u32, frame: *Frame) !String {
+        var buf: [15]u8 = undefined;
+        const name = std.fmt.bufPrint(&buf, "data-{d}", .{idx}) catch unreachable;
+        return String.init(frame.local_arena, name, .{});
+    }
+
     // The supported property names are the camel-cased names of the
     // element's data-* attributes, in attribute order.
     fn getNames(self: *DOMStringMap, frame: *Frame) !js.Array {