# Stack implementation missing length property! (found 2nd bug in Absolute Beginner’s Guide to Algorithms)

**URL:** <https://forum.kirupa.com/t/stack-implementation-missing-length-property-found-2nd-bug-in-absolute-beginner-s-guide-to-algorithms/663667>\
**Category:** programming\
**Created:** [December 14, 2023, 10:53pm UTC](https://forum.kirupa.com/t/stack-implementation-missing-length-property-found-2nd-bug-in-absolute-beginner-s-guide-to-algorithms/663667 "2023-12-14T22:53:03Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![transbot](https://avatars.discourse-cdn.com/v4/letter/t/4bbf92/32.png) [@transbot](https://forum.kirupa.com/u/transbot)\
**Post date:** [December 14, 2023, 10:53pm UTC](https://forum.kirupa.com/t/stack-implementation-missing-length-property-found-2nd-bug-in-absolute-beginner-s-guide-to-algorithms/663667/1 "2023-12-14T22:53:03Z")

</div>

Dear author,  
I hope this message finds you well. I am writing to bring to your attention a potential issue with the Stack implementation provided in your Chapter 19 DFS example (stack\_v1.js).

It appears that the Stack class lacks an implementation for the `length` property, which results in an unexpected behavior in the DFS implementation provided in Chapter 19. Specifically, the condition `while (discovered.length > 0)` does not work as intended due to the absence of the `length` property.

To address this issue, I suggest adding the following `length` method to the Stack class:

```auto
class Stack {
  constructor(...items) {
    this.items = items;
  }
  
  // ... (other methods remain unchanged)

  get length() {
    return this.items.length;
  }
}

```

This modification ensures that the DFS algorithm correctly checks for an empty stack.

Best regards

---

<div class="post-metadata">

**Author:** ![kirupa](https://yyz1.discourse-cdn.com/flex011/user_avatar/forum.kirupa.com/kirupa/32/11616_2.png) [@kirupa](https://forum.kirupa.com/u/kirupa)\
**Post date:** [December 15, 2023, 4:01am UTC](https://forum.kirupa.com/t/stack-implementation-missing-length-property-found-2nd-bug-in-absolute-beginner-s-guide-to-algorithms/663667/2 "2023-12-15T04:01:23Z")

</div>

Thanks for being thorough! I had this change queued but it somehow failed to get updated on the server. Here is the correct version: **[https://www.kirupa.com/js/stack\_v1.js?new](https://www.kirupa.com/js/stack_v1.js?new)** (I added the ?new to bypass the CDN caching!)

Below is the full implementation for easy reference:

```js
/**
 * A simple Stack implementation in JavaScript
 * 
 * Visit https://www.kirupa.com for a deep-dive on how this works!
 * 
 * Copyright 2023 Kirupa Chinnathambi (@kirupa)
 * License: MIT
 */
class Stack {
  constructor(...items) {
    // Initialize the stack with any pre-populated items.
    this.items = items;
  }

  clear() {
    // Set the length of the items array to 0 to effectively clear the stack.
    this.items.length = 0;
  }

  clone() {
    // Use the spread operator to create a new stack with a copy of the current items.
    return new Stack(...this.items);
  }

  contains(item) {
    // Check if the item exists in the stack using `includes`.
    return this.items.includes(item);
  }

  peek() {
    // Get the last item in the stack without removing it (LIFO principle).
    return this.items[this.items.length - 1];
  }

  pop() {
    // Remove and return the last item from the stack (LIFO principle).
    return this.items.pop();
  }

  push(item) {
    // Add an item to the top of the stack.
    this.items.push(item);
    return item;
  }

  get length() {
    // Return the current size of the stack (number of items).
    return this.items.length;
  }
}

```