Iterate over the tree in reverse

Author: Joris-van-der-Wel

lib/SymbolTree.js

@@ -521,12 +521,14 @@ class SymbolTree {
          * @method treeIterator
          * @memberOf module:symbol-tree#
          * @param {Object} root
+         * @param {Boolean} [reverse=false]
          * @return {Object} An iterable iterator (ES6)
          */
-        treeIterator(root) {
-                const following = this.following.bind(this);
-
-                let nextObject = root;
+        treeIterator(root, reverse) {
+                let nextObject = reverse
+                        ? this.lastInclusiveDescendant(root)
+                        : root;
+                const findNext = (reverse ? this.preceding : this.following).bind(this);
                 const iterator = {};
 
                 iterator.next = function() {
@@ -538,7 +540,7 @@ class SymbolTree {
                         }
 
                         const value = nextObject;
-                        nextObject = following(nextObject, root);
+                        nextObject = findNext(nextObject, root);
 
                         return {
                                 done  : false,

test/SymbolTree.js

@@ -978,6 +978,36 @@ test('tree iterator', function(t) {
         t.end();
 });
 
+test('tree iterator reverse', 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, true);
+
+        for (const object of iterator) {
+                results.push(object);
+        }
+        t.deepEqual([ac, abaa, aba, ab, aa, a], results);
+        t.deepEqual({done: true, value: a}, iterator.next());
+        t.deepEqual({done: true, value: a}, iterator.next()); // should keep returning done: true
+
+        t.end();
+});
+
 test('look up the index of an object', function(t) {
         const tree = new SymbolTree();
         const a = {};