Implement NodeHelpers::index()

1 files changed, 6 insertions, 0 deletions

diff --git a/components/script/dom/node.rs b/components/script/dom/node.rs
index dfe91b6e17e..9143677d1e0 100644
--- a/components/script/dom/node.rs
+++ b/components/script/dom/node.rs
@@ -428,6 +428,7 @@ pub trait NodeHelpers {
 
     fn type_id(self) -> NodeTypeId;
     fn len(self) -> u32;
+    fn index(self) -> u32;
 
     fn parent_node(self) -> Option<Temporary<Node>>;
     fn first_child(self) -> Option<Temporary<Node>>;
@@ -579,6 +580,11 @@ impl<'a> NodeHelpers for JSRef<'a, Node> {
         }
     }
 
+    // https://dom.spec.whatwg.org/#concept-tree-index
+    fn index(self) -> u32 {
+        self.preceding_siblings().count() as u32
+    }
+
     fn parent_node(self) -> Option<Temporary<Node>> {
         self.parent_node.get().map(Temporary::from_rooted)
     }