diff --git a/src/browser/dom/document.zig b/src/browser/dom/document.zig
index bc8dccbc..fe4a499a 100644
--- a/src/browser/dom/document.zig
+++ b/src/browser/dom/document.zig
@@ -18,6 +18,7 @@
 
 const std = @import("std");
 
+const log = @import("../../log.zig");
 const parser = @import("../netsurf.zig");
 const Page = @import("../page.zig").Page;
 
@@ -120,9 +121,28 @@ pub const Document = struct {
         return try Element.toInterface(e);
     }
 
-    pub fn _createElement(self: *parser.Document, tag_name: []const u8) !ElementUnion {
-        const e = try parser.documentCreateElement(self, tag_name);
-        return try Element.toInterface(e);
+    const CreateElementResult = union(enum) {
+        element: ElementUnion,
+        custom: Env.JsObject,
+    };
+
+    pub fn _createElement(self: *parser.Document, tag_name: []const u8, page: *Page) !CreateElementResult {
+        const custom_element = page.window.custom_elements._get(tag_name) orelse {
+            const e = try parser.documentCreateElement(self, tag_name);
+            return .{ .element = try Element.toInterface(e) };
+        };
+
+        var result: Env.Function.Result = undefined;
+        const js_obj = custom_element.newInstance(&result) catch |err| {
+            log.fatal(.user_script, "newInstance error", .{
+                .err = result.exception,
+                .stack = result.stack,
+                .tag_name = tag_name,
+                .source = "createElement",
+            });
+            return err;
+        };
+        return .{ .custom = js_obj };
     }
 
     pub fn _createElementNS(self: *parser.Document, ns: []const u8, tag_name: []const u8) !ElementUnion {
diff --git a/src/browser/env.zig b/src/browser/env.zig
index 7d6627ec..806391e5 100644
--- a/src/browser/env.zig
+++ b/src/browser/env.zig
@@ -33,6 +33,7 @@ const WebApis = struct {
         @import("xhr/xhr.zig").Interfaces,
         @import("xhr/form_data.zig").Interfaces,
         @import("xmlserializer/xmlserializer.zig").Interfaces,
+        @import("webcomponents/webcomponents.zig").Interfaces,
     });
 };
 
diff --git a/src/browser/html/elements.zig b/src/browser/html/elements.zig
index 3ce70361..948810a2 100644
--- a/src/browser/html/elements.zig
+++ b/src/browser/html/elements.zig
@@ -16,6 +16,7 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 const std = @import("std");
+const log = @import("../../log.zig");
 
 const parser = @import("../netsurf.zig");
 const generate = @import("../../runtime/generate.zig");
@@ -112,6 +113,10 @@ pub const HTMLElement = struct {
     pub const prototype = *Element;
     pub const subtype = .node;
 
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
+
     pub fn get_style(e: *parser.ElementHTML, page: *Page) !*CSSStyleDeclaration {
         const state = try page.getOrCreateNodeState(@ptrCast(e));
         return &state.style;
@@ -174,6 +179,10 @@ pub const HTMLMediaElement = struct {
     pub const Self = parser.MediaElement;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 // HTML elements
@@ -183,6 +192,10 @@ pub const HTMLUnknownElement = struct {
     pub const Self = parser.Unknown;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 // https://html.spec.whatwg.org/#the-a-element
@@ -191,6 +204,10 @@ pub const HTMLAnchorElement = struct {
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
 
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
+
     pub fn get_target(self: *parser.Anchor) ![]const u8 {
         return try parser.anchorGetTarget(self);
     }
@@ -428,144 +445,240 @@ pub const HTMLAppletElement = struct {
     pub const Self = parser.Applet;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLAreaElement = struct {
     pub const Self = parser.Area;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLAudioElement = struct {
     pub const Self = parser.Audio;
     pub const prototype = *HTMLMediaElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLBRElement = struct {
     pub const Self = parser.BR;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLBaseElement = struct {
     pub const Self = parser.Base;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLBodyElement = struct {
     pub const Self = parser.Body;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLButtonElement = struct {
     pub const Self = parser.Button;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLCanvasElement = struct {
     pub const Self = parser.Canvas;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLDListElement = struct {
     pub const Self = parser.DList;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLDataElement = struct {
     pub const Self = parser.Data;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLDataListElement = struct {
     pub const Self = parser.DataList;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLDialogElement = struct {
     pub const Self = parser.Dialog;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLDirectoryElement = struct {
     pub const Self = parser.Directory;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLDivElement = struct {
     pub const Self = parser.Div;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLEmbedElement = struct {
     pub const Self = parser.Embed;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLFieldSetElement = struct {
     pub const Self = parser.FieldSet;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLFontElement = struct {
     pub const Self = parser.Font;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLFrameElement = struct {
     pub const Self = parser.Frame;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLFrameSetElement = struct {
     pub const Self = parser.FrameSet;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLHRElement = struct {
     pub const Self = parser.HR;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLHeadElement = struct {
     pub const Self = parser.Head;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLHeadingElement = struct {
     pub const Self = parser.Heading;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLHtmlElement = struct {
     pub const Self = parser.Html;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLIFrameElement = struct {
     pub const Self = parser.IFrame;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLImageElement = struct {
@@ -573,6 +686,10 @@ pub const HTMLImageElement = struct {
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
 
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
+
     pub fn get_alt(self: *parser.Image) ![]const u8 {
         return try parser.imageGetAlt(self);
     }
@@ -613,6 +730,7 @@ pub const HTMLImageElement = struct {
     pub const Factory = struct {
         pub const js_name = "Image";
         pub const subtype = .node;
+
         pub const js_legacy_factory = true;
         pub const prototype = *HTMLImageElement;
 
@@ -631,6 +749,10 @@ pub const HTMLInputElement = struct {
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
 
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
+
     pub fn get_defaultValue(self: *parser.Input) ![]const u8 {
         return try parser.inputGetDefaultValue(self);
     }
@@ -719,114 +841,190 @@ pub const HTMLLIElement = struct {
     pub const Self = parser.LI;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLLabelElement = struct {
     pub const Self = parser.Label;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLLegendElement = struct {
     pub const Self = parser.Legend;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLLinkElement = struct {
     pub const Self = parser.Link;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLMapElement = struct {
     pub const Self = parser.Map;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLMetaElement = struct {
     pub const Self = parser.Meta;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLMeterElement = struct {
     pub const Self = parser.Meter;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLModElement = struct {
     pub const Self = parser.Mod;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLOListElement = struct {
     pub const Self = parser.OList;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLObjectElement = struct {
     pub const Self = parser.Object;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLOptGroupElement = struct {
     pub const Self = parser.OptGroup;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLOptionElement = struct {
     pub const Self = parser.Option;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLOutputElement = struct {
     pub const Self = parser.Output;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLParagraphElement = struct {
     pub const Self = parser.Paragraph;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLParamElement = struct {
     pub const Self = parser.Param;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLPictureElement = struct {
     pub const Self = parser.Picture;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLPreElement = struct {
     pub const Self = parser.Pre;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLProgressElement = struct {
     pub const Self = parser.Progress;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLQuoteElement = struct {
     pub const Self = parser.Quote;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 // https://html.spec.whatwg.org/#the-script-element
@@ -835,6 +1033,10 @@ pub const HTMLScriptElement = struct {
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
 
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
+
     pub fn get_src(self: *parser.Script) !?[]const u8 {
         return try parser.elementGetAttribute(
             parser.scriptToElt(self),
@@ -969,101 +1171,166 @@ pub const HTMLSourceElement = struct {
     pub const Self = parser.Source;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLSpanElement = struct {
     pub const Self = parser.Span;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLStyleElement = struct {
     pub const Self = parser.Style;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLTableElement = struct {
     pub const Self = parser.Table;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLTableCaptionElement = struct {
     pub const Self = parser.TableCaption;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLTableCellElement = struct {
     pub const Self = parser.TableCell;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLTableColElement = struct {
     pub const Self = parser.TableCol;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLTableRowElement = struct {
     pub const Self = parser.TableRow;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLTableSectionElement = struct {
     pub const Self = parser.TableSection;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLTemplateElement = struct {
     pub const Self = parser.Template;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLTextAreaElement = struct {
     pub const Self = parser.TextArea;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLTimeElement = struct {
     pub const Self = parser.Time;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLTitleElement = struct {
     pub const Self = parser.Title;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLTrackElement = struct {
     pub const Self = parser.Track;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLUListElement = struct {
     pub const Self = parser.UList;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub const HTMLVideoElement = struct {
     pub const Self = parser.Video;
     pub const prototype = *HTMLElement;
     pub const subtype = .node;
+
+    pub fn constructor(page: *Page, js_this: Env.JsThis) !*parser.Element {
+        return constructHtmlElement(page, js_this);
+    }
 };
 
 pub fn toInterface(comptime T: type, e: *parser.Element) !T {
     const elem: *align(@alignOf(*parser.Element)) parser.Element = @alignCast(e);
     const tag = try parser.elementHTMLGetTagType(@as(*parser.ElementHTML, @ptrCast(elem)));
+
     return switch (tag) {
         .abbr, .acronym, .address, .article, .aside, .b, .basefont, .bdi, .bdo, .bgsound, .big, .center, .cite, .code, .dd, .details, .dfn, .dt, .em, .figcaption, .figure, .footer, .header, .hgroup, .i, .isindex, .keygen, .kbd, .main, .mark, .marquee, .menu, .menuitem, .nav, .nobr, .noframes, .noscript, .rp, .rt, .ruby, .s, .samp, .section, .small, .spacer, .strike, .strong, .sub, .summary, .sup, .tt, .u, .wbr, ._var => .{ .HTMLElement = @as(*parser.ElementHTML, @ptrCast(elem)) },
         .a => .{ .HTMLAnchorElement = @as(*parser.Anchor, @ptrCast(elem)) },
@@ -1135,6 +1402,16 @@ pub fn toInterface(comptime T: type, e: *parser.Element) !T {
     };
 }
 
+fn constructHtmlElement(page: *Page, js_this: Env.JsThis) !*parser.Element {
+    const constructor_name = try js_this.constructorName(page.call_arena);
+    if (!page.window.custom_elements.lookup.contains(constructor_name)) {
+        return error.IllegalContructor;
+    }
+
+    const el = try parser.documentCreateElement(@ptrCast(page.window.document), constructor_name);
+    return el;
+}
+
 const testing = @import("../../testing.zig");
 test "Browser.HTML.Element" {
     var runner = try testing.jsRunner(testing.tracking_allocator, .{});
diff --git a/src/browser/html/window.zig b/src/browser/html/window.zig
index f2fd3a18..74fa28b3 100644
--- a/src/browser/html/window.zig
+++ b/src/browser/html/window.zig
@@ -33,6 +33,7 @@ const EventTarget = @import("../dom/event_target.zig").EventTarget;
 const MediaQueryList = @import("media_query_list.zig").MediaQueryList;
 const Performance = @import("performance.zig").Performance;
 const CSSStyleDeclaration = @import("../cssom/css_style_declaration.zig").CSSStyleDeclaration;
+const CustomElementRegistry = @import("../webcomponents/custom_element_registry.zig").CustomElementRegistry;
 
 const storage = @import("../storage/storage.zig");
 
@@ -58,6 +59,7 @@ pub const Window = struct {
     console: Console = .{},
     navigator: Navigator = .{},
     performance: Performance,
+    custom_elements: CustomElementRegistry = .{},
 
     pub fn create(target: ?[]const u8, navigator: ?Navigator) !Window {
         var fbs = std.io.fixedBufferStream("");
@@ -163,6 +165,10 @@ pub const Window = struct {
         return &self.performance;
     }
 
+    pub fn get_customElements(self: *Window) *CustomElementRegistry {
+        return &self.custom_elements;
+    }
+
     pub fn _requestAnimationFrame(self: *Window, cbk: Function, page: *Page) !u32 {
         return self.createTimeout(cbk, 5, page, .{ .animation_frame = true });
     }
diff --git a/src/browser/page.zig b/src/browser/page.zig
index 396022db..368a3c5a 100644
--- a/src/browser/page.zig
+++ b/src/browser/page.zig
@@ -352,8 +352,23 @@ pub const Page = struct {
                 continue;
             }
 
-            const e = parser.nodeToElement(next.?);
+            const current = next.?;
+
+            const e = parser.nodeToElement(current);
             const tag = try parser.elementHTMLGetTagType(@as(*parser.ElementHTML, @ptrCast(e)));
+
+            // if (tag == .undef) {
+            //     const tag_name = try parser.nodeLocalName(@ptrCast(e));
+            //     const custom_elements = &self.window.custom_elements;
+            //     if (custom_elements._get(tag_name)) |construct| {
+            //         try construct.printFunc();
+            //         // This is just here for testing for now.
+            //         // var result: Env.Function.Result = undefined;
+            //         // _ = try construct.newInstance(*parser.Element, &result);
+            //         log.info(.browser, "Registered WebComponent Found", .{ .element_name = tag_name });
+            //     }
+            // }
+
             if (tag != .script) {
                 // ignore non-js script.
                 continue;
diff --git a/src/browser/webcomponents/custom_element_registry.zig b/src/browser/webcomponents/custom_element_registry.zig
new file mode 100644
index 00000000..3e429a67
--- /dev/null
+++ b/src/browser/webcomponents/custom_element_registry.zig
@@ -0,0 +1,91 @@
+// Copyright (C) 2023-2024  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+const log = @import("../../log.zig");
+const v8 = @import("v8");
+
+const Env = @import("../env.zig").Env;
+const Page = @import("../page.zig").Page;
+
+const Element = @import("../dom/element.zig").Element;
+
+pub const CustomElementRegistry = struct {
+    // tag_name -> Function
+    lookup: std.StringHashMapUnmanaged(Env.Function) = .empty,
+
+    pub fn _define(self: *CustomElementRegistry, tag_name: []const u8, fun: Env.Function, page: *Page) !void {
+        log.info(.browser, "define custom element", .{ .name = tag_name });
+
+        const arena = page.arena;
+        const gop = try self.lookup.getOrPut(arena, tag_name);
+        if (!gop.found_existing) {
+            errdefer _ = self.lookup.remove(tag_name);
+            const owned_tag_name = try arena.dupe(u8, tag_name);
+            gop.key_ptr.* = owned_tag_name;
+        }
+        gop.value_ptr.* = fun;
+        fun.setName(tag_name);
+    }
+
+    pub fn _get(self: *CustomElementRegistry, name: []const u8) ?Env.Function {
+        return self.lookup.get(name);
+    }
+};
+
+const testing = @import("../../testing.zig");
+
+test "Browser.CustomElementRegistry" {
+    var runner = try testing.jsRunner(testing.tracking_allocator, .{});
+    defer runner.deinit();
+    try runner.testCases(&.{
+        // Basic registry access
+        .{ "typeof customElements", "object" },
+        .{ "customElements instanceof CustomElementRegistry", "true" },
+
+        // Define a simple custom element
+        .{
+            \\ class MyElement extends HTMLElement {
+            \\   constructor() {
+            \\      super();
+            \\      this.textContent = 'Hello World';
+            \\   }
+            \\ }
+            ,
+            null,
+        },
+        .{ "customElements.define('my-element', MyElement)", "undefined" },
+
+        // Check if element is defined
+        .{ "customElements.get('my-element') === MyElement", "true" },
+        // .{ "customElements.get('non-existent')", "null" },
+
+        // Create element via document.createElement
+        .{ "let el = document.createElement('my-element')", "undefined" },
+        .{ "el instanceof MyElement", "true" },
+        .{ "el instanceof HTMLElement", "true" },
+        .{ "el.tagName", "MY-ELEMENT" },
+        .{ "el.textContent", "Hello World" },
+
+        // Create element via HTML parsing
+        // .{ "document.body.innerHTML = '<my-element></my-element>'", "undefined" },
+        // .{ "let parsed = document.querySelector('my-element')", "undefined" },
+        // .{ "parsed instanceof MyElement", "true" },
+        // .{ "parsed.textContent", "Hello World" },
+    }, .{});
+}
diff --git a/src/browser/webcomponents/webcomponents.zig b/src/browser/webcomponents/webcomponents.zig
new file mode 100644
index 00000000..2ba2a30f
--- /dev/null
+++ b/src/browser/webcomponents/webcomponents.zig
@@ -0,0 +1,23 @@
+// Copyright (C) 2023-2024  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const CustomElementRegistry = @import("custom_element_registry.zig").CustomElementRegistry;
+
+pub const Interfaces = .{
+    CustomElementRegistry,
+};
diff --git a/src/runtime/js.zig b/src/runtime/js.zig
index 2a3e5635..083b86e3 100644
--- a/src/runtime/js.zig
+++ b/src/runtime/js.zig
@@ -1257,6 +1257,16 @@ pub fn Env(comptime State: type, comptime WebApis: type) type {
                 exception: []const u8,
             };
 
+            pub fn getName(self: *const Function, allocator: Allocator) ![]const u8 {
+                const name = self.func.castToFunction().getName();
+                return valueToString(allocator, name, self.js_context.isolate, self.js_context.v8_context);
+            }
+
+            pub fn setName(self: *const Function, name: []const u8) void {
+                const v8_name = v8.String.initUtf8(self.js_context.isolate, name);
+                self.func.castToFunction().setName(v8_name);
+            }
+
             pub fn withThis(self: *const Function, value: anytype) !Function {
                 const this_obj = if (@TypeOf(value) == JsObject)
                     value.js_obj
@@ -1271,6 +1281,33 @@ pub fn Env(comptime State: type, comptime WebApis: type) type {
                 };
             }
 
+            pub fn newInstance(self: *const Function, result: *Result) !JsObject {
+                const context = self.js_context;
+
+                var try_catch: TryCatch = undefined;
+                try_catch.init(context);
+                defer try_catch.deinit();
+
+                // This creates a new instance using this Function as a constructor.
+                // This returns a generic Object
+                const js_obj = self.func.castToFunction().initInstance(context.v8_context, &.{}) orelse {
+                    if (try_catch.hasCaught()) {
+                        const allocator = context.call_arena;
+                        result.stack = try_catch.stack(allocator) catch null;
+                        result.exception = (try_catch.exception(allocator) catch "???") orelse "???";
+                    } else {
+                        result.stack = null;
+                        result.exception = "???";
+                    }
+                    return error.JsConstructorFailed;
+                };
+
+                return .{
+                    .js_context = context,
+                    .js_obj = js_obj,
+                };
+            }
+
             pub fn call(self: *const Function, comptime T: type, args: anytype) !T {
                 return self.callWithThis(T, self.getThis(), args);
             }
@@ -1450,6 +1487,11 @@ pub fn Env(comptime State: type, comptime WebApis: type) type {
                     .js_obj = array.castTo(v8.Object),
                 };
             }
+
+            pub fn constructorName(self: JsObject, allocator: Allocator) ![]const u8 {
+                const str = try self.js_obj.getConstructorName();
+                return jsStringToZig(allocator, str, self.js_context.isolate);
+            }
         };
 
         // This only exists so that we know whether a function wants the opaque
@@ -1472,6 +1514,10 @@ pub fn Env(comptime State: type, comptime WebApis: type) type {
             pub fn set(self: JsThis, key: []const u8, value: anytype, opts: JsObject.SetOpts) !void {
                 return self.obj.set(key, value, opts);
             }
+
+            pub fn constructorName(self: JsThis, allocator: Allocator) ![]const u8 {
+                return try self.obj.constructorName(allocator);
+            }
         };
 
         pub const TryCatch = struct {
@@ -1784,7 +1830,7 @@ pub fn Env(comptime State: type, comptime WebApis: type) type {
                     // a constructor function, we'll return an error.
                     if (@hasDecl(Struct, "constructor") == false) {
                         const iso = caller.isolate;
-                        const js_exception = iso.throwException(createException(iso, "illegal constructor"));
+                        const js_exception = iso.throwException(createException(iso, "Illegal Constructor"));
                         info.getReturnValue().set(js_exception);
                         return;
                     }
@@ -2543,6 +2589,7 @@ fn Caller(comptime E: type, comptime State: type) type {
             var js_err: ?v8.Value = switch (err) {
                 error.InvalidArgument => createTypeException(isolate, "invalid argument"),
                 error.OutOfMemory => createException(isolate, "out of memory"),
+                error.IllegalConstructor => createException(isolate, "Illegal Contructor"),
                 else => blk: {
                     const func = @field(Struct, named_function.name);
                     const return_type = @typeInfo(@TypeOf(func)).@"fn".return_type orelse {
@@ -2656,8 +2703,8 @@ fn Caller(comptime E: type, comptime State: type) type {
                 // a JS argument
                 if (comptime isJsThis(params[params.len - 1].type.?)) {
                     @field(args, std.fmt.comptimePrint("{d}", .{params.len - 1 + offset})) = .{ .obj = .{
+                        .js_context = js_context,
                         .js_obj = info.getThis(),
-                        .executor = self.executor,
                     } };
 
                     // AND the 2nd last parameter is state