Array Deletion at End in DSA Javascript - Execution Trace

Concept Flow - Array Deletion at End

Start with array

↓

Check if array is empty?

Yes→Stop, nothing to delete

No↓

Remove last element

↓

Update array size

↓

End with updated array

The flow starts with checking if the array is empty. If not, it removes the last element and updates the array size.

Execution Sample

DSA Javascript

let arr = [10, 20, 30, 40];
arr.pop();
console.log(arr);

This code removes the last element from the array and prints the updated array.

Execution Table

Step	Operation	Array Before	Action	Array After	Pointer Changes	Visual State
1	Start	[10, 20, 30, 40]	Check if empty	[10, 20, 30, 40]	head=0, tail=3	10 -> 20 -> 30 -> 40 -> null
2	Delete last element	[10, 20, 30, 40]	Remove element at tail index 3	[10, 20, 30]	tail=2	10 -> 20 -> 30 -> null
3	End	[10, 20, 30]	Print array	[10, 20, 30]	tail=2	10 -> 20 -> 30 -> null

💡 Deletion stops after removing the last element; array size reduced by 1.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
arr	[10, 20, 30, 40]	[10, 20, 30, 40]	[10, 20, 30]	[10, 20, 30]
tail	3	3	2	2
head	0	0	0	0
length	4	4	3	3

Key Moments - 3 Insights

Why do we check if the array is empty before deleting?

Because deleting from an empty array would cause an error or unexpected behavior. Step 1 in the execution_table shows this check.

What happens to the array size after deletion?

The array size decreases by one. Step 2 shows the tail pointer moving from 3 to 2, reflecting the new size.

Does the head pointer change when deleting the last element?

No, the head pointer remains at 0 because deletion at the end does not affect the start of the array, as shown in variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table, what is the array state after Step 2?

A [10, 20, 30]

B [10, 20, 30, 40]

C [20, 30, 40]

D []

💡 Hint

Check the 'Array After' column in Step 2 of the execution_table.

At which step does the tail pointer change?

A Step 1

B Step 3

C Step 2

D Tail pointer never changes

💡 Hint

Look at the 'Pointer Changes' column in the execution_table.

If the array was empty at start, what would happen?

A Deletion proceeds and array becomes empty

B Deletion stops immediately, no change

C Array size increases

D Error occurs and program crashes

💡 Hint

Refer to the concept_flow and Step 1 in execution_table about empty array check.

Concept Snapshot

Array Deletion at End:
- Use pop() to remove last element
- Check if array is empty before deleting
- Tail pointer moves left by one
- Head pointer stays same
- Array size decreases by one

Full Transcript

This visual execution shows how deleting the last element from an array works. First, we check if the array is empty to avoid errors. Then we remove the last element by reducing the tail pointer and array size by one. The head pointer remains unchanged. The updated array is printed at the end.

Practice

1. What does the pop() method do to an array in JavaScript?

easy

A. Returns the length of the array without modifying it

B. Removes the last element from the array and returns it

C. Adds a new element to the end of the array

D. Removes the first element from the array and returns it

Solution

1. Step 1: Understand the pop() method

   The pop() method removes the last element from an array and returns that element.

2. Step 2: Compare with other array methods

   Unlike shift() which removes the first element, pop() targets the end of the array.

3. Final Answer:

   Removes the last element from the array and returns it -> Option B

4. Quick Check:

   pop() removes last element [OK]

Hint: pop() always removes the last item from the array [OK]

Common Mistakes:

• Confusing pop() with shift() which removes the first element
• Thinking pop() adds elements instead of removing
• Assuming pop() returns the array length

2. Which of the following is the correct syntax to remove the last element from an array named arr?

easy

A. pop(arr);

B. arr.removeLast();

C. arr.pop();

D. arr.deleteLast();

Solution

1. Step 1: Identify the correct method for array end deletion

   JavaScript arrays use the pop() method to remove the last element.

2. Step 2: Check method call syntax

   The correct syntax is calling pop() directly on the array object: arr.pop();

3. Final Answer:

   arr.pop(); -> Option C

4. Quick Check:

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

Hint: Use arr.pop() to remove last element [OK]

Common Mistakes:

• Using non-existent methods like removeLast() or deleteLast()
• Calling pop() as a standalone function instead of on the array
• Using incorrect syntax like pop(arr)

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

const arr = [10, 20, 30, 40];
const removed = arr.pop();
console.log(arr);
console.log(removed);

medium

A. [10, 20, 30, 40] and 30

B. [10, 20, 30, 40] and 40

C. [10, 20, 30] and 30

D. [10, 20, 30] and 40

Solution

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

   The pop() method removes the last element (40) from arr and returns it.

2. Step 2: Check the console outputs

   After popping, arr becomes [10, 20, 30] and removed stores 40.

3. Final Answer:

   [10, 20, 30] and 40 -> Option D

4. Quick Check:

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

Hint: pop() returns removed last element, array shrinks by one [OK]

Common Mistakes:

• Expecting pop() to remove first element
• Confusing returned value with new last element
• Thinking array remains unchanged after pop()

4. Identify the error in the following code that tries to remove the last element from an array:

const numbers = [1, 2, 3, 4];
numbers.pop(2);
console.log(numbers);

medium

A. pop() does not take any arguments; passing 2 is incorrect

B. pop() should be called as pop(numbers)

C. pop() removes the first element, so this code is wrong

D. pop() returns the new array, so console.log will be empty

Solution

1. Step 1: Check pop() method signature

   The pop() method does not accept any arguments; it always removes the last element.

2. Step 2: Analyze the code behavior

   Passing 2 as an argument does nothing and is incorrect usage, but JavaScript ignores it and still removes the last element.

3. Final Answer:

   pop() does not take any arguments; passing 2 is incorrect -> Option A

4. Quick Check:

   pop() takes no arguments [OK]

Hint: pop() never needs arguments to remove last element [OK]

Common Mistakes:

• Passing arguments to pop() expecting to remove specific elements
• Calling pop() as a standalone function
• Assuming pop() removes first element

5. Given the array let fruits = ['apple', 'banana', 'cherry', 'date'];, which code snippet correctly removes the last two elements and stores them in a new array removedFruits in the same order as they appeared in the original array?

hard

A. const removedFruits = fruits.splice(-2);

B. const removedFruits = fruits.pop(2);

C. const removedFruits = [fruits.pop(), fruits.pop()];

D. const removedFruits = fruits.shift(2);

Solution

1. Step 1: Understand pop() vs splice() for multiple deletions

   The pop() method removes only one element at a time. To remove multiple elements, splice() is used.

2. Step 2: Analyze each option

   const removedFruits = [fruits.pop(), fruits.pop()]; removes two elements but stores them in reverse order; const removedFruits = fruits.pop(2); is invalid as pop() takes no arguments; const removedFruits = fruits.splice(-2); correctly removes last two elements and returns them as an array in original order; const removedFruits = fruits.shift(2); uses shift() incorrectly.

3. Final Answer:

   const removedFruits = fruits.splice(-2); -> Option A

4. Quick Check:

   splice(-2) removes last two elements as array [OK]

Hint: Use splice(-2) to remove last two elements at once [OK]

Common Mistakes:

• Using pop() with arguments to remove multiple elements
• Confusing shift() with pop() for end deletion
• Expecting pop() to return an array of removed elements