添加二叉树的迭代遍历javaScript版本

problems/二叉树的迭代遍历.md

@@ -330,6 +330,70 @@ func inorderTraversal(root *TreeNode) []int {
 }
 ```
 
+javaScript
+
+```js
+
+前序遍历:
+
+// 入栈 右 -> 左
+// 出栈 中 -> 左 -> 右
+var preorderTraversal = function(root, res = []) {
+    if(!root) return res;
+    const stack = [root];
+    let cur = null;
+    while(stack.length) {
+        cur = stack.pop();
+        res.push(cur.val);
+        cur.right && stack.push(cur.right);
+        cur.left && stack.push(cur.left);
+    }
+    return res;
+};
+
+中序遍历:
+
+// 入栈 左 -> 右
+// 出栈 左 -> 中 -> 右
+
+var inorderTraversal = function(root, res = []) {
+    const stack = [];
+    let cur = root;
+    while(stack.length || cur) {
+        if(cur) {
+            stack.push(cur);
+            // 左
+            cur = cur.left;
+        } else {
+            // --> 弹出 中
+            cur = stack.pop();
+            res.push(cur.val); 
+            // 右
+            cur = cur.right;
+        }
+    };
+    return res;
+};
+
+后序遍历:
+
+// 入栈 左 -> 右
+// 出栈 中 -> 右 -> 左 结果翻转
+
+var postorderTraversal = function(root, res = []) {
+    if (!root) return res;
+    const stack = [root];
+    let cur = null;
+    do {
+        cur = stack.pop();
+        res.push(cur.val);
+        cur.left && stack.push(cur.left);
+        cur.right && stack.push(cur.right);
+    } while(stack.length);
+    return res.reverse();
+};
+```
+
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)