Iterate over a tree using an ES6 iterator

Author: Joris-van-der-Wel

lib/SymbolTree.js

@@ -306,7 +306,7 @@ class SymbolTree {
         /**
          * Iterate over all children of the given object to an array.
          *
-         * `O(1)` (per iterate step)
+         * `O(1)` for a single iteration
          *
          * @method childrenIterator
          * @memberOf module:symbol-tree#
@@ -343,6 +343,47 @@ class SymbolTree {
                 return iterator;
         }
 
+        /**
+         * Iterate over all descendants of the given object (in tree order).
+         *
+         * `O(n)` for the entire iteration<br>
+         * `O(n)` for a single iteration (worst case)
+         *
+         * @method treeIterator
+         * @memberOf module:symbol-tree#
+         * @param {Object} root
+         * @return {Object} An iterable iterator (ES6)
+         */
+        treeIterator(root) {
+                const following = this.following.bind(this);
+
+                let nextObject = root;
+                const iterator = {};
+
+                iterator.next = function() {
+                        if (!nextObject) {
+                                return {
+                                        done  : true,
+                                        value : root
+                                };
+                        }
+
+                        const value = nextObject;
+                        nextObject = following(nextObject, root);
+
+                        return {
+                                done  : false,
+                                value : value
+                        };
+                };
+
+                iterator[Symbol.iterator] = function() {
+                        return iterator;
+                };
+
+                return iterator;
+        }
+
         /**
          * Remove the object from this tree.
          * Has no effect if already removed.

test/SymbolTree.js

@@ -782,3 +782,33 @@ test('treeToArray with filter', function(t) {
 
         t.end();
 });
+
+test('tree iterator', function(t) {
+        const tree = new SymbolTree();
+        const a = {};
+        const aa = {};
+        const ab = {};
+        const aba = {};
+        const abaa = {};
+        const ac = {};
+        const b = {};
+
+        tree.insertLast(aa, a);
+        tree.insertLast(ab, a);
+        tree.insertLast(aba, ab);
+        tree.insertLast(abaa, aba);
+        tree.insertLast(ac, a);
+        tree.insertAfter(b, a);
+
+        const results = [];
+        const iterator = tree.treeIterator(a);
+
+        for (const object of iterator) {
+                results.push(object);
+        }
+        t.deepEqual([a, aa, ab, aba, abaa, ac], results);
+        t.deepEqual({done: true, value: a}, iterator.next());
+        t.deepEqual({done: true, value: a}, iterator.next()); // should keep returning done: true
+
+        t.end();
+});