Push Using Linked List Node in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node with the given value.

DSA Javascript

class Node {
  constructor(value) {
    this.value = [1];
    this.next = null;
  }
}

Drag options to blanks, or click blank then click option'

Anode

Bval

Cvalue

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong variable name like 'val' or 'node' instead of 'value'.

The constructor parameter is named 'value', so we assign it to this.value.

2fill in blank

medium

Complete the code to set the new node's next pointer to the current head.

DSA Javascript

function push(head, value) {
  const newNode = new Node(value);
  newNode.next = [1];
  return newNode;
}

Drag options to blanks, or click blank then click option'

Ahead

Bvalue

Cnull

DnewNode

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to null loses the existing list.

Setting next to value or newNode causes errors.

The new node's next should point to the current head to insert it at the front.

3fill in blank

hard

Fix the error in the push function to correctly add a new node at the front.

DSA Javascript

function push(head, value) {
  const newNode = new Node(value);
  newNode.next = [1];
  return newNode;
}

Drag options to blanks, or click blank then click option'

Avalue

Bhead

Cnull

DnewNode

Attempts:

3 left

💡 Hint

Common Mistakes

Returning head instead of newNode causes the list not to update.

The new node's next should point to head, but the function must return newNode to update the list head.

4fill in blank

hard

Fill both blanks to complete the push function that adds a new node at the front and returns it.

DSA Javascript

function push(head, value) {
  const newNode = new Node([1]);
  newNode.next = [2];
  return newNode;
}

Drag options to blanks, or click blank then click option'

Avalue

Bhead

Cnull

DnewNode

Attempts:

3 left

💡 Hint

Common Mistakes

Using null for next loses the existing list.

Using newNode for next causes a cycle.

The new node is created with the given value and its next points to the current head.

5fill in blank

hard

Fill all three blanks to implement push that creates a new node, links it, and returns it.

DSA Javascript

function push(head, value) {
  const newNode = new Node([1]);
  newNode.next = [2];
  return [3];
}

Drag options to blanks, or click blank then click option'

Ahead

Bvalue

CnewNode

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Returning head instead of newNode.

Setting next to null loses the list.

Create newNode with value, link next to head, and return newNode as new list head.

Practice

1. What does the push operation do in a linked list when using nodes?

easy

A. Removes the last node from the list

B. Adds a new node at the beginning of the list

C. Searches for a node with a specific value

D. Deletes the first node of the list

Solution

1. Step 1: Understand push operation in linked list

   The push operation adds a new node to the start (head) of the linked list.

2. Step 2: Compare with other operations

   Removing or searching nodes are different operations, not push.

3. Final Answer:

   Adds a new node at the beginning of the list -> Option B

4. Quick Check:

   Push = Add at head [OK]

Hint: Push always adds node at the start of the list [OK]

Common Mistakes:

• Confusing push with pop or delete
• Thinking push adds at the end
• Mixing push with search operation

2. Which of the following is the correct syntax to create a new node and push it to the front of a linked list in JavaScript?

easy

A. newNode = Node(value); head = newNode.next;

B. head = new Node(value); head.next = newNode;

C. let newNode = new Node(value); newNode.next = head; head = newNode;

D. head.next = new Node(value); head = head.next;

Solution

1. Step 1: Create new node and link it to current head

   We create a new node, set its next to current head, then update head to new node.

2. Step 2: Check each option

   let newNode = new Node(value); newNode.next = head; head = newNode; correctly does this. Others either reverse assignments or miss new keyword.

3. Final Answer:

   let newNode = new Node(value); newNode.next = head; head = newNode; -> Option C

4. Quick Check:

   New node points to old head, head updated [OK]

Hint: New node's next points to old head, then update head [OK]

Common Mistakes:

• Forgetting to use 'new' keyword
• Assigning head before setting newNode.next
• Mixing order of assignments

3. What will be the linked list after executing the following code?

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

let head = null;

function push(value) {
  let newNode = new Node(value);
  newNode.next = head;
  head = newNode;
}

push(10);
push(20);
push(30);

medium

A. 10 -> 20 -> 30 -> null

B. null -> 10 -> 20 -> 30

C. 20 -> 30 -> 10 -> null

D. 30 -> 20 -> 10 -> null

Solution

1. Step 1: Trace push calls and list updates

   First push(10): head = 10 -> null
   Second push(20): head = 20 -> 10 -> null
   Third push(30): head = 30 -> 20 -> 10 -> null

2. Step 2: Confirm final linked list order

   New nodes are added at front, so list is 30 -> 20 -> 10 -> null.

3. Final Answer:

   30 -> 20 -> 10 -> null -> Option D

4. Quick Check:

   Last pushed is first in list [OK]

Hint: Last pushed node becomes new head [OK]

Common Mistakes:

• Assuming push adds at end
• Confusing order of nodes
• Ignoring that head updates each push

4. Identify the error in the following push function for a linked list:

function push(value) {
  let newNode = Node(value);
  newNode.next = head;
  head = newNode;
}

medium

A. Missing 'new' keyword when creating newNode

B. Incorrect assignment of newNode.next

C. head should be assigned before newNode.next

D. Function should return the new head

Solution

1. Step 1: Check node creation syntax

   Node is a class; must use 'new' keyword to create instance. Missing here.

2. Step 2: Verify other assignments

   newNode.next = head and head = newNode are correct order and assignments.

3. Final Answer:

   Missing 'new' keyword when creating newNode -> Option A

4. Quick Check:

   Use 'new' to create class instance [OK]

Hint: Always use 'new' with class constructors [OK]

Common Mistakes:

• Forgetting 'new' causes runtime error
• Swapping assignment order
• Expecting push to return head

5. Given a linked list with nodes 5 -> 15 -> 25 -> null, what will be the list after pushing a new node with value 10 using the push function?

function push(value) {
  let newNode = new Node(value);
  newNode.next = head;
  head = newNode;
}

Assume head points to the first node (5).

medium

A. 10 -> 5 -> 15 -> 25 -> null

B. 5 -> 15 -> 25 -> 10 -> null

C. 5 -> 10 -> 15 -> 25 -> null

D. 25 -> 15 -> 5 -> 10 -> null

Solution

1. Step 1: Understand push adds node at front

   Push creates new node with value 10, sets its next to current head (5), then updates head to new node.

2. Step 2: Visualize new list order

   New head is 10, followed by old list 5 -> 15 -> 25 -> null, so final list is 10 -> 5 -> 15 -> 25 -> null.

3. Final Answer:

   10 -> 5 -> 15 -> 25 -> null -> Option A

4. Quick Check:

   Push adds new node at front [OK]

Hint: Push inserts new node before current head [OK]

Common Mistakes:

• Appending new node at end instead of front
• Not updating head pointer
• Mixing node order after push