Use an options argument instead of various arguments, for preceding()

Author: Joris-van-der-Wel

lib/SymbolTree.js

@@ -174,12 +174,15 @@ class SymbolTree {
          * @method preceding
          * @memberOf module:symbol-tree#
          * @param {Object} object
-         * @param {Object} [treeRoot] If set, `treeRoot` must be an inclusive ancestor
+         * @param {Object} [options]
+         * @param {Object} [options.root] If set, `root` must be an inclusive ancestor
          *        of the return value (or else null is returned). This check _assumes_
          *        that `root` is also an inclusive ancestor of the given `node`
          * @returns {?Object}
          */
-        preceding(object, treeRoot) {
+        preceding(object, options) {
+                const treeRoot = options && options.root;
+
                 if (object === treeRoot) {
                         return null;
                 }

lib/TreeIterator.js

@@ -37,7 +37,7 @@ class TreeIterator {
                         this[NEXT] = tree._node(value).parent;
                 }
                 else if (iterateFunc === 4) {
-                        this[NEXT] = tree.preceding(value, root);
+                        this[NEXT] = tree.preceding(value, {root: root});
                 }
                 else /*if (iterateFunc === 5)*/ {
                         this[NEXT] = tree.following(value, root);

test/SymbolTree.js

@@ -517,9 +517,9 @@ test('look up preceding using a specified root', function(t) {
 
         tree.insertLast(aa, a);
 
-        t.equal(null, tree.preceding(a, a));
-        t.equal(a   , tree.preceding(aa, a));
-        t.equal(null, tree.preceding(aa, aa));
+        t.equal(null, tree.preceding(a , {root: a}));
+        t.equal(a   , tree.preceding(aa, {root: a}));
+        t.equal(null, tree.preceding(aa, {root: aa}));
 
         t.end();
 });