add the solution of Maximum Depth of Binary Tree(104) with Javascript.

Author: QianYuTing

README.md

@@ -75,7 +75,7 @@
 | [088][088-question] | [Merge Sorted Array][088-tips]                               | [Easy][E]   | [✅][088-java] | [✅][088-js] | [✅][088-kotlin] |
 | [100][100-question] | [Same Tree][100-tips]                                        | [Easy][E]   | [✅][100-java] | [✅][100-js] | [✅][100-kotlin] |
 | [101][101-question] | [Symmetric Tree][101-tips]                                   | [Easy][E]   | [✅][101-java] | [✅][101-js] | [✅][101-kotlin] |
-| [104][104-question] | [Maximum Depth of Binary Tree][104-tips]                     | [Easy][E]   | [✅][104-java] |              | [✅][104-kotlin] |
+| [104][104-question] | [Maximum Depth of Binary Tree][104-tips]                     | [Easy][E]   | [✅][104-java] | [✅][104-js] | [✅][104-kotlin] |
 | [107][107-question] | [Binary Tree Level Order Traversal II][107-tips]             | [Easy][E]   | [✅][107-java] |              | [✅][107-kotlin] |
 | [108][108-question] | [Convert Sorted Array to Binary Search Tree][108-tips]       | [Easy][E]   | [✅][108-java] |              | [✅][108-kotlin] |
 | [110][110-question] | [Balanced Binary Tree][110-tips]                             | [Easy][E]   | [✅][110-java] |              | [✅][110-kotlin] |
@@ -455,6 +455,7 @@ commit信息模板: ``feat: add the solution of `Two Sum`(001) with Java``
 [088-js]: ./src/_088/Solution.js
 [100-js]: ./src/_100/Solution.js
 [101-js]: ./src/_101/Solution.js
+[104-js]: ./src/_104/Solution.js
 [226-js]: ./src/_226/Solution.js
 [561-js]: ./src/_561/Solution.js
 [643-js]: ./src/_643/Solution.js

src/_104/Solution.js

@@ -0,0 +1,15 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number}
+ */
+var maxDepth = function(root) {
+    if (root == null) return 0;
+     return 1 + Math.max(maxDepth(root.left), maxDepth(root.right));
+};