add JavaScript codes for Tree

codes/javascript/include/TreeNode.js

@@ -0,0 +1,47 @@
+/**
+ * File: TreeNode.js
+ * Created Time: 2022-12-04
+ * Author: IsChristina (christinaxia77@foxmail.com)
+ */
+
+/**
+ * Definition for a binary tree node.
+ */
+function TreeNode(val, left, right) {
+    this.val = (val === undefined ? 0 : val) // 结点值
+    this.left = (left === undefined ? null : left) // 左子结点指针
+    this.right = (right === undefined ? null : right) // 右子结点指针
+}
+
+/**
+* Generate a binary tree with an array
+* @param arr
+* @return
+*/
+function arrToTree(arr) {
+    if (arr.length === 0)
+        return null;
+         
+    let root = new TreeNode(arr[0]);
+    let queue = [root] 
+    let i = 1;
+    while(queue.length) {
+        let node = queue.shift();
+        if(arr[i] !== null) {
+            node.left = new TreeNode(arr[i]);
+            queue.push(node.left);
+        }
+        i++;
+        if(arr[i] !== null) {
+            node.right = new TreeNode(arr[i]);
+            queue.push(node.right);
+        }
+        i++;
+    }
+    return root;
+}
+
+module.exports = { 
+    TreeNode,
+    arrToTree,
+}