Added Tree_Postorder_Traversal implementation in JavaScript. (jainama…

…n224#1978)

* Added Tree_Postorder_Traversal in JavaScript.

Tree_Postorder_Traversal/Tree_Postorder_Traversal.js

@@ -0,0 +1,38 @@
+/*
+ * Program to traverse a tree in Post Order.
+ */
+
+// Creates a Tree Node with input value.
+class Node {
+    constructor(value) {
+        this.value = value;
+        this.left = null;
+        this.right = null;
+    }
+}
+
+// Function for POST ORDER Tree Transversal.
+function PostOrder(root) {
+    if (root) {
+        PostOrder(root.left);
+        PostOrder(root.right);
+        console.log(root.value);
+    }
+}
+
+// Sample Input.
+var root = new Node(1);
+root.left = new Node(2);
+root.right = new Node(3);
+root.left.left = new Node(4);
+root.left.right = new Node(5);
+root.right.left = new Node(6);
+root.right.right = new Node(7);
+
+// Sample Output
+console.log("Post Order traversal of tree is:-");
+PostOrder(root);
+
+/*
+ * Expected Output:- 4 5 2 6 7 3 1
+ */