improve traverse perf by using for-loops

index.js

@@ -20,21 +20,21 @@ function parse (src, opts) {
 
 var traverse = function (node, cb) {
     if (Array.isArray(node)) {
-        node.forEach(function (x) {
-            if(x != null) {
-                x.parent = node;
-                traverse(x, cb);
+        for (var i = 0; i < node.length; i++) {
+            if (node[i] != null) {
+                node[i].parent = node;
+                traverse(node[i], cb);
             }
-        });
+        }
     }
     else if (node && typeof node === 'object') {
         cb(node);
-
-        Object.keys(node).forEach(function (key) {
-            if (key === 'parent' || !node[key]) return;
+        for (var key in node) {
+            if (!node.hasOwnProperty(key)) continue;
+            if (key === 'parent' || !node[key]) continue;
             node[key].parent = node;
             traverse(node[key], cb);
-        });
+        }
     }
 };