A little confused about the While condition in `doubly-linked-list.js` insertBefore and insertAfter

[lchtao26]

~/computer-science-in-javascript/src/data-structures/doubly-linked-list/doubly-linked-list.js

    insertBefore(data, index) {
            // ...omit other lines util here
            // line 183
            while ((current.next !== null) && (i < index)) {
                current = current.next;
                i++;
            }
        }

    insertAfter(data, index) {
        // ...omit other lines util here
        // line 259
        while ((current !== null) && (i < index)) {
            current = current.next;
            i++;
        }

I am confused about the difference of while condition between line 183 and 259,

and do a test in node for the insertAfter method:

const { DoublyLinkedListi } = require( "./doubly-linked-list.js");
const doublyLinkedList = new DoublyLinkedList();

doublyLinkedList.add(1);
doublyLinkedList.insertAfter(1, 1);

and it will throw an the error below, it's not a expected error throw by the doubly Linked List class.

            current.next.previous = newNode;
                    ^
TypeError: Cannot read property 'next' of null

So I think current.next !== null in insertBefore method is right for insertAfter, instead of current !== null

[IAmAnubhavSaini]

In your function call doublyLinkedList.insertAfter(1, 1);; the second 1 is index. Index 1 doesn't exist just after one add().

const { DoublyLinkedList } = require( "./doubly-linked-list.js");
const doublyLinkedList = new DoublyLinkedList();

doublyLinkedList.add(1);
doublyLinkedList.add(2);
doublyLinkedList.add(3);
doublyLinkedList.insertAfter(10, 1);

for(let i of doublyLinkedList.values())
    console.log(i)

// 1, 2, 10, 3

[lchtao26]

It is, the index 1 doesn't exist. I do it on purpose. My point is, if the index is exceed, the error should be throw by insertAfter function as:

        // line 270
        if (i < index) {
            throw new RangeError(`Index ${index} does not exist in the list.`);
        }

and should not be throw by the the exception.

            current.next.previous = newNode;
                    ^
TypeError: Cannot read property 'next' of null

I think that is caused by the while condition current !== null

[mikro03]

~/computer-science-in-javascript/src/data-structures/doubly-linked-list/doubly-linked-list.js

    insertBefore(data, index) {
            // ...omit other lines util here
            // line 183
            while ((current.next !== null) && (i < index)) {
                current = current.next;
                i++;
            }
        }

    insertAfter(data, index) {
        // ...omit other lines util here
        // line 259
        while ((current !== null) && (i < index)) {
            current = current.next;
            i++;
        }

I am confused about the difference of while condition between line 183 and 259,

and do a test in node for the insertAfter method:

const { DoublyLinkedListi } = require( "./doubly-linked-list.js");
const doublyLinkedList = new DoublyLinkedList();

doublyLinkedList.add(1);
doublyLinkedList.insertAfter(1, 1);

and it will throw an the error below, it's not a expected error throw by the doubly Linked List class.

            current.next.previous = newNode;
                    ^
TypeError: Cannot read property 'next' of null

So I think current.next !== null in insertBefore method is right for insertAfter, instead of current !== null

[mithleshgupta]

Can you assign this to me

[BajiShaik07]

class Node {
constructor(data) {
this.data = data;
this.next = null;
this.prev = null;
}
}

class DoublyLinkedList {
constructor() {
this.head = null;
this.tail = null;
}

insertBefore(nodeToInsert, node) {
if (nodeToInsert === null) return;

if (node === this.head) {
  nodeToInsert.next = this.head;
  this.head.prev = nodeToInsert;
  this.head = nodeToInsert;
} else {
  nodeToInsert.prev = node.prev;
  nodeToInsert.next = node;
  node.prev.next = nodeToInsert;
  node.prev = nodeToInsert;
}

}

insertAfter(nodeToInsert, node) {
if (nodeToInsert === null) return;

if (node === this.tail) {
  nodeToInsert.prev = this.tail;
  this.tail.next = nodeToInsert;
  this.tail = nodeToInsert;
} else {
  nodeToInsert.prev = node;
  nodeToInsert.next = node.next;
  node.next.prev = nodeToInsert;
  node.next = nodeToInsert;
}

}
}