fix(js): keep TreeWalker traversal in document order (#432)

crates/obscura-js/js/bootstrap.js

@@ -2611,18 +2611,10 @@ class Document extends Node {
         return true;
       },
       nextNode() {
-        let node = this.currentNode;
-        let child = node.firstChild;
-        while (child) {
-          if (this._accept(child)) { this.currentNode = child; return child; }
-          if (child.firstChild) { child = child.firstChild; continue; }
-          if (child.nextSibling) { child = child.nextSibling; continue; }
-          let parent = child.parentNode;
-          while (parent && parent !== this.root) {
-            if (parent.nextSibling) { child = parent.nextSibling; break; }
-            parent = parent.parentNode;
-          }
-          if (!parent || parent === this.root) return null;
+        let node = _wrap(+_dom("next_in_subtree", this.root._nid, this.currentNode._nid));
+        while (node) {
+          if (this._accept(node)) { this.currentNode = node; return node; }
+          node = _wrap(+_dom("next_in_subtree", this.root._nid, node._nid));
         }
         return null;
       },

crates/obscura-js/src/ops.rs

@@ -268,6 +268,13 @@ fn op_dom_inner(state: &OpState, cmd: String, arg1: String, arg2: String) -> Str
                 "prev_sibling" => n.prev_sibling, _ => None,
             }).flatten().map(|id| id.index().to_string()).unwrap_or("-1".into())
         }
+        "next_in_subtree" => {
+            let root = NodeId::new(arg1.parse::<u32>().unwrap_or(0));
+            let current = NodeId::new(arg2.parse::<u32>().unwrap_or(0));
+            dom.next_in_subtree(root, current)
+                .map(|id| id.index().to_string())
+                .unwrap_or("-1".into())
+        }
         "child_nodes" => {
             let nid = arg1.parse::<u32>().unwrap_or(0);
             let ids: Vec<i32> = dom.children(NodeId::new(nid)).iter().map(|id| id.index() as i32).collect();