Pop Operation on Stack in DSA Javascript - Build from Scratch

Pop Operation on Stack

📖 Scenario: Imagine you have a stack of books. You can only take the top book off the stack at a time. This is how a stack data structure works in programming.

🎯 Goal: You will create a stack using an array, set up a variable to hold the stack, perform a pop operation to remove the top item, and then print the stack after the pop.

📋 What You'll Learn

Create an array called stack with these exact values: ['book1', 'book2', 'book3', 'book4']

Create a variable called poppedItem to store the result of the pop operation

Use the pop() method on stack to remove the top item and assign it to poppedItem

Print the stack array after the pop operation

💡 Why This Matters

🌍 Real World

Stacks are used in many real-world applications like undo features in text editors, browser history, and managing function calls.

💼 Career

Understanding stack operations like pop is essential for software development roles, especially when working with algorithms, parsing, and memory management.

1

Create the stack array

Create an array called stack with these exact values: ['book1', 'book2', 'book3', 'book4']

DSA Javascript

// Create the stack array with the given books
// Your code here

Hint

Use const stack = ['book1', 'book2', 'book3', 'book4']; to create the stack.

2

Set up variable for pop result

Create a variable called poppedItem to store the result of the pop operation from stack

DSA Javascript

const stack = ['book1', 'book2', 'book3', 'book4'];
// Create variable poppedItem to hold popped value
// Your code here

Hint

Use let poppedItem; to declare the variable before popping.

3

Pop the top item from the stack

Use the pop() method on stack to remove the top item and assign it to poppedItem

DSA Javascript

const stack = ['book1', 'book2', 'book3', 'book4'];
let poppedItem;
// Pop the top item from stack and assign to poppedItem
// Your code here

Hint

Use poppedItem = stack.pop(); to remove and store the top item.

4

Print the stack after pop

Print the stack array after the pop operation using console.log(stack)

DSA Javascript

const stack = ['book1', 'book2', 'book3', 'book4'];
let poppedItem;
poppedItem = stack.pop();
// Print the stack array after pop
// Your code here

Hint

Use console.log(stack); to show the stack after popping.

Practice

1. What does the pop() operation do in a stack?

easy

A. Removes and returns the top element of the stack

B. Adds a new element to the bottom of the stack

C. Returns the bottom element without removing it

D. Clears all elements from the stack

Solution

1. Step 1: Understand stack behavior

   A stack follows Last In First Out (LIFO) principle, so the last added element is on top.

2. Step 2: Define pop operation

   The pop operation removes and returns the top element of the stack, following LIFO.

3. Final Answer:

   Removes and returns the top element of the stack -> Option A

4. Quick Check:

   pop() = remove top element [OK]

Hint: Pop always removes the last added item [OK]

Common Mistakes:

• Thinking pop adds elements
• Confusing pop with peek (which only returns)
• Assuming pop removes bottom element

2. Which of the following is the correct syntax to pop an element from a stack implemented as an array in JavaScript?

easy

A. pop(stack);

B. stack.popElement();

C. stack.pop();

D. stack.remove();

Solution

1. Step 1: Recall JavaScript array pop method

   JavaScript arrays have a built-in method pop() to remove the last element.

2. Step 2: Match correct syntax

   The correct syntax to pop from an array named stack is stack.pop();

3. Final Answer:

   stack.pop(); -> Option C

4. Quick Check:

   Use array.pop() to remove last element [OK]

Hint: Use array.pop() to remove top stack element [OK]

Common Mistakes:

• Using non-existent methods like popElement()
• Calling pop as a standalone function
• Using remove() which is not valid for arrays

3. What will be the output of the following code?

const stack = [10, 20, 30];
const popped = stack.pop();
console.log(popped);
console.log(stack);

medium

A. 20
[10, 20, 30]

B. undefined
[10, 20]

C. 30
[10, 20, 30]

D. 30
[10, 20]

Solution

1. Step 1: Understand pop() effect on array

   pop() removes the last element (30) and returns it, so popped is 30.

2. Step 2: Check stack after pop

   After pop, stack becomes [10, 20] because 30 is removed.

3. Final Answer:

   30 [10, 20] -> Option D

4. Quick Check:

   pop() returns last element and removes it [OK]

Hint: pop() returns last item and removes it from array [OK]

Common Mistakes:

• Expecting pop() to return second last element
• Assuming stack remains unchanged after pop
• Confusing pop() return value with stack content

4. Identify the error in the following code snippet that tries to pop an element from a stack:

let stack = [1, 2, 3];
let popped = stack.pop;
console.log(popped);

medium

A. pop is not a function

B. pop method is not called, missing parentheses

C. stack is not defined

D. pop returns undefined always

Solution

1. Step 1: Check how pop is used

   The code assigns stack.pop without parentheses, so it assigns the function itself, not the result.

2. Step 2: Correct usage of pop

   To pop and get the value, pop must be called with parentheses: stack.pop().

3. Final Answer:

   pop method is not called, missing parentheses -> Option B

4. Quick Check:

   Use stack.pop() to call pop method [OK]

Hint: Always use parentheses to call pop() method [OK]

Common Mistakes:

• Forgetting parentheses when calling pop
• Thinking pop is a property, not a function
• Assuming pop returns undefined without call

5. Given a stack implemented as an array stack = [5, 10, 15], what will be the state of the stack after performing two consecutive pop() operations?

hard

A. [5]

B. [10]

C. [5, 10]

D. []

Solution

1. Step 1: Perform first pop()

   First pop removes 15, stack becomes [5, 10].

2. Step 2: Perform second pop()

   Second pop removes 10, stack becomes [5].

3. Final Answer:

   [5] -> Option A

4. Quick Check:

   Two pops remove last two elements [OK]

Hint: Each pop removes one top element [OK]

Common Mistakes:

• Removing elements from the bottom instead of top
• Assuming pop does not change stack
• Confusing number of pops with elements removed