添加二叉树的递归遍历javascript版本

problems/二叉树的递归遍历.md

@@ -272,6 +272,41 @@ func PostorderTraversal(root *TreeNode) (res []int) {
 }
 ```
 
+javaScript:
+
+```js
+
+前序遍历:
+
+var preorderTraversal = function(root, res = []) {
+    if (!root) return res;
+    res.push(root.val);
+    preorderTraversal(root.left, res)
+    preorderTraversal(root.right, res)
+    return res;
+};
+
+中序遍历:
+
+var inorderTraversal = function(root, res = []) {
+    if (!root) return res;
+    inorderTraversal(root.left, res);
+    res.push(root.val);
+    inorderTraversal(root.right, res);
+    return res;
+};
+
+后序遍历:
+
+var postorderTraversal = function(root, res = []) {
+    if (!root) return res;
+    postorderTraversal(root.left, res);
+    postorderTraversal(root.right, res);
+    res.push(root.val);
+    return res;
+};
+```
+