3 files changed, 31 insertions, 1 deletions
diff --git a/components/script/dom/htmltableelement.rs b/components/script/dom/htmltableelement.rs
index 4ea908675b1..efcc24f4370 100644
--- a/components/script/dom/htmltableelement.rs
+++ b/components/script/dom/htmltableelement.rs
@@ -118,6 +118,13 @@ impl HTMLTableElement {
             thead.upcast::<Node>().remove_self();
         }
     }
+
+    /// Determine the row index for the given `HTMLTableRowElement`.
+    pub fn row_index(&self, row_elem: &HTMLTableRowElement) -> Option<usize> {
+        self.Rows()
+            .elements_iter()
+            .position(|elem| (&elem as &Element) == row_elem.upcast::<Element>())
+    }
 }
 
 impl HTMLTableElementMethods for HTMLTableElement {
diff --git a/components/script/dom/htmltablerowelement.rs b/components/script/dom/htmltablerowelement.rs
index be0a9c9f5fb..c6d532a0323 100644
--- a/components/script/dom/htmltablerowelement.rs
+++ b/components/script/dom/htmltablerowelement.rs
@@ -14,7 +14,9 @@ use dom::element::{Element, RawLayoutElementHelpers};
 use dom::htmlcollection::{CollectionFilter, HTMLCollection};
 use dom::htmlelement::HTMLElement;
 use dom::htmltabledatacellelement::HTMLTableDataCellElement;
+use dom::htmltableelement::HTMLTableElement;
 use dom::htmltableheadercellelement::HTMLTableHeaderCellElement;
+use dom::htmltablesectionelement::HTMLTableSectionElement;
 use dom::node::{Node, window_from_node};
 use dom::virtualmethods::VirtualMethods;
 use string_cache::Atom;
@@ -87,6 +89,27 @@ impl HTMLTableRowElementMethods for HTMLTableRowElement {
             || self.Cells(),
             |n| n.is::<HTMLTableDataCellElement>())
     }
+
+    // https://html.spec.whatwg.org/multipage/#dom-tr-rowindex
+    fn RowIndex(&self) -> i32 {
+        let parent = match self.upcast::<Node>().GetParentNode() {
+            Some(parent) => parent,
+            None => return -1,
+        };
+        if let Some(table) = parent.downcast::<HTMLTableElement>() {
+            return table.row_index(self).map_or(-1, |i| i as i32);
+        }
+        if !parent.is::<HTMLTableSectionElement>() {
+            return -1;
+        }
+        let grandparent = match parent.upcast::<Node>().GetParentNode() {
+            Some(parent) => parent,
+            None => return -1,
+        };
+        grandparent.downcast::<HTMLTableElement>()
+                   .and_then(|table| table.row_index(self))
+                   .map_or(-1, |i| i as i32)
+    }
 }
 
 pub trait HTMLTableRowElementLayoutHelpers {
diff --git a/components/script/dom/webidls/HTMLTableRowElement.webidl b/components/script/dom/webidls/HTMLTableRowElement.webidl
index 66538630c9d..05d339aba3f 100644
--- a/components/script/dom/webidls/HTMLTableRowElement.webidl
+++ b/components/script/dom/webidls/HTMLTableRowElement.webidl
@@ -5,7 +5,7 @@
 
 // https://html.spec.whatwg.org/multipage/#htmltablerowelement
 interface HTMLTableRowElement : HTMLElement {
-  //readonly attribute long rowIndex;
+  readonly attribute long rowIndex;
   //readonly attribute long sectionRowIndex;
   readonly attribute HTMLCollection cells;
   [Throws]