diff --git a/components/script/dom/node.rs b/components/script/dom/node.rs
index 23914d3f407..dfe91b6e17e 100644
--- a/components/script/dom/node.rs
+++ b/components/script/dom/node.rs
@@ -427,6 +427,7 @@ pub trait NodeHelpers {
     fn is_parent_of(self, child: JSRef<Node>) -> bool;
 
     fn type_id(self) -> NodeTypeId;
+    fn len(self) -> u32;
 
     fn parent_node(self) -> Option<Temporary<Node>>;
     fn first_child(self) -> Option<Temporary<Node>>;
@@ -567,6 +568,17 @@ impl<'a> NodeHelpers for JSRef<'a, Node> {
         self.type_id
     }
 
+    // https://dom.spec.whatwg.org/#concept-node-length
+    fn len(self) -> u32 {
+        match self.type_id {
+            NodeTypeId::DocumentType => 0,
+            NodeTypeId::CharacterData(_) => {
+                CharacterDataCast::to_ref(self).unwrap().Length()
+            },
+            _ => self.children().count() as u32
+        }
+    }
+
     fn parent_node(self) -> Option<Temporary<Node>> {
         self.parent_node.get().map(Temporary::from_rooted)
     }