From 20b0c48e849df92c4a04965f9df7038f980a256c Mon Sep 17 00:00:00 2001
From: Oleksii Trekhleb <trehleb@gmail.com>
Date: Wed, 22 Aug 2018 07:49:22 +0300
Subject: [PATCH] Add comments to Stack code.

---
 src/data-structures/stack/Stack.js | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/data-structures/stack/Stack.js b/src/data-structures/stack/Stack.js
index 664df053..762b428e 100644
--- a/src/data-structures/stack/Stack.js
+++ b/src/data-structures/stack/Stack.js
@@ -2,6 +2,9 @@ import LinkedList from '../linked-list/LinkedList';
 
 export default class Stack {
   constructor() {
+    // We're going to implement Queue based on LinkedList since this
+    // structures a quite similar. Compare push/pop operations of the Stack
+    // with append/deleteTail operations of LinkedList.
     this.linkedList = new LinkedList();
   }
 
@@ -9,6 +12,7 @@ export default class Stack {
    * @return {boolean}
    */
   isEmpty() {
+    // The queue is empty in case if its linked list don't have tail.
     return !this.linkedList.tail;
   }
 
@@ -17,9 +21,11 @@ export default class Stack {
    */
   peek() {
     if (this.isEmpty()) {
+      // If linked list is empty then there is nothing to peek from.
       return null;
     }
 
+    // Just read the value from the end of linked list without deleting it.
     return this.linkedList.tail.value;
   }
 
@@ -27,6 +33,8 @@ export default class Stack {
    * @param {*} value
    */
   push(value) {
+    // Pushing means to lay the value on top of the stack. Therefore let's just add
+    // new value at the end of the linked list.
     this.linkedList.append(value);
   }
 
@@ -34,6 +42,8 @@ export default class Stack {
    * @return {*}
    */
   pop() {
+    // Let's try to delete the last node from linked list (the tail).
+    // If there is no tail in linked list (it is empty) just return null.
     const removedTail = this.linkedList.deleteTail();
     return removedTail ? removedTail.value : null;
   }