Expose live computed CSS variables to scripts

crates/obscura-js/js/bootstrap.js

@@ -81,7 +81,19 @@ globalThis.dispatchEvent = function(event) {
   return !event.defaultPrevented;
 };
 
-const _dom = (cmd, a1, a2) => Deno.core.ops.op_dom(cmd, String(a1 ?? ""), String(a2 ?? ""));
+let _domMutationEpoch = 0;
+const _DOM_MUTATION_COMMANDS = new Set([
+  "append_child", "insert_before", "remove_child",
+  "set_attribute", "remove_attribute",
+  "set_text_content", "set_inner_html", "set_inner_html_context",
+  "create_element", "create_text_node", "create_comment_node",
+  "create_document_fragment", "clone_node",
+]);
+const _dom = (cmd, a1, a2) => {
+  const result = Deno.core.ops.op_dom(cmd, String(a1 ?? ""), String(a2 ?? ""));
+  if (_DOM_MUTATION_COMMANDS.has(cmd)) _domMutationEpoch++;
+  return result;
+};
 
 const _nativeFns = new Set();
 // Exact toString override for members whose native form is not just
@@ -2556,6 +2568,23 @@ class Element extends Node {
     return this.getAttribute("href") || "";
   }
   set href(v) { this.setAttribute("href", v); }
+  // HTMLHyperlinkElementUtils / HTMLAnchorElement reflected content
+  // attributes. Real-world locale, routing, and analytics code commonly
+  // enumerates `[hreflang]` links and reads the IDL property rather than
+  // getAttribute(); leaving it undefined aborts the entire component even
+  // though the attribute is present in the DOM.
+  get hreflang() { return this.getAttribute("hreflang") || ""; }
+  set hreflang(v) { this.setAttribute("hreflang", v); }
+  get rel() { return this.getAttribute("rel") || ""; }
+  set rel(v) { this.setAttribute("rel", v); }
+  get target() { return this.getAttribute("target") || ""; }
+  set target(v) { this.setAttribute("target", v); }
+  get download() { return this.getAttribute("download") || ""; }
+  set download(v) { this.setAttribute("download", v); }
+  get ping() { return this.getAttribute("ping") || ""; }
+  set ping(v) { this.setAttribute("ping", v); }
+  get referrerPolicy() { return this.getAttribute("referrerpolicy") || ""; }
+  set referrerPolicy(v) { this.setAttribute("referrerpolicy", v); }
   // HTMLHyperlinkElementUtils URL-decomposition members, live on <a>/<area>.
   get protocol() { const u = (this.localName === 'a' || this.localName === 'area') ? _elemHrefURL(this) : null; return u ? u.protocol : ''; }
   set protocol(v) { if (this.localName === 'a' || this.localName === 'area') _setElemHrefPart(this, 'protocol', v); }
@@ -5863,12 +5892,21 @@ globalThis.getComputedStyle = (el) => {
   // cascade/layout. Fetch it once per CSSStyleDeclaration proxy: reading a
   // dozen properties must not trigger a dozen layout/native crossings.
   let rendered = null;
-  if (typeof Deno.core.ops.op_computed_style === 'function' && el?._nid != null) {
-    try {
-      const raw = Deno.core.ops.op_computed_style(String(el._nid | 0));
-      rendered = raw ? JSON.parse(raw) : null;
-    } catch (e) {}
-  }
+  let renderedEpoch = -1;
+  let computedNames = [];
+  const refreshRendered = () => {
+    if (renderedEpoch === _domMutationEpoch) return;
+    renderedEpoch = _domMutationEpoch;
+    rendered = null;
+    if (typeof Deno.core.ops.op_computed_style === 'function' && el?._nid != null) {
+      try {
+        const raw = Deno.core.ops.op_computed_style(String(el._nid | 0));
+        rendered = raw ? JSON.parse(raw) : null;
+      } catch (e) {}
+    }
+    computedNames = rendered ? Object.keys(rendered) : [];
+  };
+  refreshRendered();
   // React virtualization libraries (react-window, tanstack-virtual,
   // react-virtuoso) all compute container dimensions via getComputedStyle.
   // The defaults table previously returned `auto` for width/height and
@@ -5924,6 +5962,7 @@ globalThis.getComputedStyle = (el) => {
 
   const lookup = (rawProp) => {
     if (typeof rawProp !== 'string') return '';
+    refreshRendered();
     const kebab = rawProp.replace(/([A-Z])/g, '-$1').toLowerCase();
     if (rendered && Object.prototype.hasOwnProperty.call(rendered, kebab))
       return rendered[kebab];
@@ -5944,8 +5983,14 @@ globalThis.getComputedStyle = (el) => {
       if (prop === Symbol.toPrimitive || prop === Symbol.toStringTag) return undefined;
       if (prop === 'getPropertyValue') return (name) => lookup(name);
       if (prop === 'getPropertyPriority') return () => '';
-      if (prop === 'item') return (i) => '';
-      if (prop === 'length') return 0;
+      if (prop === 'item') return (i) => {
+        refreshRendered();
+        return computedNames[i | 0] || '';
+      };
+      if (prop === 'length') {
+        refreshRendered();
+        return computedNames.length;
+      }
       if (prop === 'cssText') return '';
       if (prop === 'parentRule') return null;
       // CSSStyleDeclaration's `has` trap intentionally reports every known

crates/obscura-js/src/ops.rs

@@ -2473,10 +2473,23 @@ fn op_computed_style(state: &OpState, #[string] nid_str: String) -> String {
     let nid: u32 = nid_str.parse().unwrap_or(0);
     let nid = obscura_dom::tree::NodeId::new(nid);
     let mut gs = shared.borrow_mut();
-    ensure_prepared_render(&mut gs)
-        .and_then(|prepared| prepared.computed_style(nid))
-        .and_then(|snapshot| serde_json::to_string(&snapshot).ok())
-        .unwrap_or_default()
+    let Some(prepared) = ensure_prepared_render(&mut gs) else {
+        return String::new();
+    };
+    let Some(snapshot) = prepared.computed_style(nid) else {
+        return String::new();
+    };
+    let custom = prepared
+        .computed_custom_properties(nid)
+        .unwrap_or_default();
+    let mut object = serde_json::Map::with_capacity(snapshot.len() + custom.len());
+    for (name, value) in snapshot {
+        object.insert(name.to_string(), serde_json::Value::String(value));
+    }
+    for (name, value) in custom {
+        object.insert(name, serde_json::Value::String(value));
+    }
+    serde_json::Value::Object(object).to_string()
 }
 
 /// Root scrolling overflow in CSS pixels. The JS CSSOM probes this op only in

crates/obscura-js/src/runtime.rs

@@ -2168,6 +2168,52 @@ mod tests {
         );
     }
 
+    #[test]
+    fn hyperlink_content_attributes_reflect_through_the_idl_surface() {
+        let mut rt = setup_runtime(
+            r#"<html><body>
+                <a id="locale" hreflang="en-US" rel="alternate"
+                   target="_blank" download="guide.pdf"
+                   ping="/audit" referrerpolicy="no-referrer">English</a>
+            </body></html>"#,
+        );
+        let result = rt
+            .evaluate(
+                r#"
+                const link = document.getElementById("locale");
+                const initial = [
+                    link.hreflang, link.rel, link.target, link.download,
+                    link.ping, link.referrerPolicy,
+                    link.hreflang.split("-")[1]
+                ];
+                link.hreflang = "de-DE";
+                link.referrerPolicy = "origin";
+                return [
+                    initial,
+                    link.getAttribute("hreflang"),
+                    link.getAttribute("referrerpolicy")
+                ];
+                "#,
+            )
+            .unwrap();
+        assert_eq!(
+            result,
+            serde_json::json!([
+                [
+                    "en-US",
+                    "alternate",
+                    "_blank",
+                    "guide.pdf",
+                    "/audit",
+                    "no-referrer",
+                    "US"
+                ],
+                "de-DE",
+                "origin"
+            ])
+        );
+    }
+
     #[cfg(feature = "render")]
     #[test]
     fn computed_style_uses_renderer_stylesheet_cascade_and_invalidates() {
@@ -2239,6 +2285,78 @@ mod tests {
         );
     }
 
+    #[cfg(feature = "render")]
+    #[test]
+    fn computed_style_exposes_cascaded_custom_properties_and_invalidates() {
+        let dom = parse_html(
+            r#"<html><head><style>
+                :root { --inherited-space: 17px; --derived-space: var(--inherited-space); }
+                #nav {
+                    --r-globalnav-font-size:17px;
+                    --local-scale:1.25;
+                    font-size:var(--r-globalnav-font-size);
+                }
+            </style></head><body>
+                <nav id="nav"><span id="child"></span></nav>
+            </body></html>"#,
+        );
+        let mut rt = ObscuraJsRuntime::new();
+        rt.set_dom(dom);
+        rt.set_viewport(400.0, 200.0);
+        rt.run_page_init();
+
+        assert_eq!(
+            rt.evaluate(
+                r#"
+                const nav = document.getElementById("nav");
+                const child = document.getElementById("child");
+                const navStyle = getComputedStyle(nav);
+                const childStyle = getComputedStyle(child);
+                let enumeratesBase = false;
+                for (let i = 0; i < navStyle.length; i++) {
+                    if (navStyle.item(i) === "--r-globalnav-font-size")
+                        enumeratesBase = true;
+                }
+                return [
+                    navStyle.fontSize,
+                    navStyle.getPropertyValue("--r-globalnav-font-size"),
+                    parseInt(navStyle.fontSize) /
+                        parseInt(navStyle.getPropertyValue("--r-globalnav-font-size")),
+                    navStyle.getPropertyValue("--inherited-space"),
+                    navStyle.getPropertyValue("--derived-space"),
+                    navStyle.getPropertyValue("--local-scale"),
+                    childStyle.getPropertyValue("--inherited-space"),
+                    childStyle.getPropertyValue("--local-scale"),
+                    enumeratesBase
+                ];
+                "#,
+            )
+            .unwrap(),
+            serde_json::json!([
+                "17px", "17px", 1,
+                "17px", "17px", "1.25", "17px", "1.25", true
+            ])
+        );
+
+        assert_eq!(
+            rt.evaluate(
+                r#"
+                const nav = document.getElementById("nav");
+                const computed = getComputedStyle(nav);
+                nav.style.setProperty("--inherited-space", "23px");
+                nav.style.fontSize = "19px";
+                return [
+                    computed.fontSize,
+                    computed.getPropertyValue("--inherited-space"),
+                    computed.getPropertyValue("--derived-space")
+                ];
+                "#,
+            )
+            .unwrap(),
+            serde_json::json!(["19px", "23px", "17px"])
+        );
+    }
+
     #[tokio::test(flavor = "current_thread")]
     async fn idle_event_loop_flushes_resolved_promise_continuations() {
         let mut rt = setup_runtime("<html><body><div id='state'>pending</div></body></html>");