1 files changed, 27 insertions, 25 deletions

diff --git a/components/script/dom/element.rs b/components/script/dom/element.rs
index 8132011a0fe..1944d1d030e 100644
--- a/components/script/dom/element.rs
+++ b/components/script/dom/element.rs
@@ -70,7 +70,7 @@ use selectors::parser::{AttrSelector, NamespaceConstraint};
 use smallvec::VecLike;
 use std::ascii::AsciiExt;
 use std::borrow::{Cow, ToOwned};
-use std::cell::{Ref, RefMut};
+use std::cell::Ref;
 use std::default::Default;
 use std::mem;
 use std::sync::Arc;
@@ -92,6 +92,7 @@ pub struct Element {
     namespace: Namespace,
     prefix: Option<DOMString>,
     attrs: DOMRefCell<Vec<JS<Attr>>>,
+    id_attribute: DOMRefCell<Option<Atom>>,
     style_attribute: DOMRefCell<Option<PropertyDeclarationBlock>>,
     attr_list: MutNullableHeap<JS<NamedNodeMap>>,
     class_list: MutNullableHeap<JS<DOMTokenList>>,
@@ -146,6 +147,7 @@ impl Element {
             attrs: DOMRefCell::new(vec!()),
             attr_list: Default::default(),
             class_list: Default::default(),
+            id_attribute: DOMRefCell::new(None),
             style_attribute: DOMRefCell::new(None),
         }
     }
@@ -505,6 +507,7 @@ pub trait LayoutElementHelpers {
     unsafe fn html_element_in_html_document_for_layout(&self) -> bool;
     #[allow(unsafe_code)]
     unsafe fn has_attr_for_layout(&self, namespace: &Namespace, name: &Atom) -> bool;
+    fn id_attribute(&self) -> *const Option<Atom>;
     fn style_attribute(&self) -> *const Option<PropertyDeclarationBlock>;
     fn local_name(&self) -> &Atom;
     fn namespace(&self) -> &Namespace;
@@ -529,6 +532,13 @@ impl LayoutElementHelpers for LayoutJS<Element> {
     }
 
     #[allow(unsafe_code)]
+    fn id_attribute(&self) -> *const Option<Atom> {
+        unsafe {
+            (*self.unsafe_get()).id_attribute.borrow_for_layout()
+        }
+    }
+
+    #[allow(unsafe_code)]
     fn style_attribute(&self) -> *const Option<PropertyDeclarationBlock> {
         unsafe {
             (*self.unsafe_get()).style_attribute.borrow_for_layout()
@@ -610,10 +620,6 @@ impl Element {
         self.attrs.borrow()
     }
 
-    pub fn attrs_mut(&self) -> RefMut<Vec<JS<Attr>>> {
-        self.attrs.borrow_mut()
-    }
-
     pub fn style_attribute(&self) -> &DOMRefCell<Option<PropertyDeclarationBlock>> {
         &self.style_attribute
     }
@@ -1484,6 +1490,15 @@ impl VirtualMethods for Element {
                 NodeDamage::NodeStyleDamaged
             },
             &atom!(id) => {
+                *self.id_attribute.borrow_mut() =
+                    mutation.new_value(attr).and_then(|value| {
+                        let value = value.as_atom();
+                        if value != &atom!("") {
+                            Some(value.clone())
+                        } else {
+                            None
+                        }
+                    });
                 if node.is_in_doc() {
                     let value = attr.value().as_atom().clone();
                     match mutation {
@@ -1530,13 +1545,9 @@ impl VirtualMethods for Element {
 
         if !tree_in_doc { return; }
 
-        if let Some(ref attr) = self.get_attribute(&ns!(""), &atom!("id")) {
-            let value = attr.value();
-            if !value.is_empty() {
-                let doc = document_from_node(self);
-                let value = Atom::from_slice(&value);
-                doc.register_named_element(self, value.to_owned());
-            }
+        if let Some(ref value) = *self.id_attribute.borrow() {
+            let doc = document_from_node(self);
+            doc.register_named_element(self, value.clone());
         }
     }
 
@@ -1547,13 +1558,9 @@ impl VirtualMethods for Element {
 
         if !tree_in_doc { return; }
 
-        if let Some(ref attr) = self.get_attribute(&ns!(""), &atom!("id")) {
-            let value = attr.value();
-            if !value.is_empty() {
-                let doc = document_from_node(self);
-                let value = Atom::from_slice(&value);
-                doc.unregister_named_element(self, value.to_owned());
-            }
+        if let Some(ref value) = *self.id_attribute.borrow() {
+            let doc = document_from_node(self);
+            doc.unregister_named_element(self, value.clone());
         }
     }
 }
@@ -1639,12 +1646,7 @@ impl<'a> ::selectors::Element for Root<Element> {
         node.get_focus_state()
     }
     fn get_id(&self) -> Option<Atom> {
-        self.get_attribute(&ns!(""), &atom!("id")).map(|attr| {
-            match *attr.r().value() {
-                AttrValue::Atom(ref val) => val.clone(),
-                _ => panic!("`id` attribute should be AttrValue::Atom"),
-            }
-        })
+        self.id_attribute.borrow().clone()
     }
     fn get_disabled_state(&self) -> bool {
         let node = NodeCast::from_ref(&**self);