2 files changed, 31 insertions, 1 deletions
diff --git a/components/script/dom/htmlselectelement.rs b/components/script/dom/htmlselectelement.rs
index 03d10e117f4..c44dac71000 100644
--- a/components/script/dom/htmlselectelement.rs
+++ b/components/script/dom/htmlselectelement.rs
@@ -299,6 +299,36 @@ impl HTMLSelectElementMethods for HTMLSelectElement {
             opt.set_selectedness(false);
         }
     }
+
+    // https://html.spec.whatwg.org/multipage/#dom-select-selectedindex
+    fn SelectedIndex(&self) -> i32 {
+        self.upcast::<Node>()
+            .traverse_preorder()
+            .filter_map(Root::downcast::<HTMLOptionElement>)
+            .enumerate()
+            .filter(|&(_, ref opt_elem)| opt_elem.Selected())
+            .map(|(i, _)| i as i32)
+            .next()
+            .unwrap_or(-1)
+    }
+
+    // https://html.spec.whatwg.org/multipage/#dom-select-selectedindex
+    fn SetSelectedIndex(&self, index: i32) {
+        let mut opt_iter = self.upcast::<Node>()
+                               .traverse_preorder()
+                               .filter_map(Root::downcast::<HTMLOptionElement>);
+        for opt in opt_iter.by_ref().take(index as usize) {
+            opt.set_selectedness(false);
+        }
+        if let Some(opt) = opt_iter.next() {
+            opt.set_selectedness(true);
+            opt.set_dirtiness(true);
+            // Reset remaining <option> elements
+            for opt in opt_iter {
+                opt.set_selectedness(false);
+            }
+        }
+    }
 }
 
 impl VirtualMethods for HTMLSelectElement {
diff --git a/components/script/dom/webidls/HTMLSelectElement.webidl b/components/script/dom/webidls/HTMLSelectElement.webidl
index a8fd2803c44..543c3267c64 100644
--- a/components/script/dom/webidls/HTMLSelectElement.webidl
+++ b/components/script/dom/webidls/HTMLSelectElement.webidl
@@ -25,7 +25,7 @@ interface HTMLSelectElement : HTMLElement {
   //setter void (unsigned long index, HTMLOptionElement? option);
 
   //readonly attribute HTMLCollection selectedOptions;
-  //         attribute long selectedIndex;
+  attribute long selectedIndex;
   attribute DOMString value;
 
   //readonly attribute boolean willValidate;