Array Deletion at Beginning in DSA Javascript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after deleting the first element?

Consider the following JavaScript code that deletes the first element of an array. What will be the printed output?

DSA Javascript

let arr = [10, 20, 30, 40];
arr.shift();
console.log(arr.join(' -> ') + ' -> null');

A 20 -> 30 -> 40 -> null

B 10 -> 20 -> 30 -> 40 -> null

C Error: shift is not a function

D 30 -> 40 -> null

💡 Hint

The shift() method removes the first element of the array.

The shift() method removes the first element (10) from the array, so the remaining elements are 20, 30, and 40.

❓ Predict Output

intermediate

What happens if we delete the first element from an empty array?

What will be the output of the following code?

DSA Javascript

let arr = [];
arr.shift();
console.log(arr.length);

A undefined

B 1

C 0

D Error: Cannot shift from empty array

💡 Hint

Removing from an empty array does not cause an error.

Calling shift() on an empty array returns undefined but does not change the array length, which remains 0.

❓ Predict Output

advanced

What is the output after multiple deletions at the beginning?

What will be printed after running this code?

DSA Javascript

let arr = [5, 10, 15, 20, 25];
arr.shift();
arr.shift();
console.log(arr.join(' -> ') + ' -> null');

A 10 -> 15 -> 20 -> 25 -> null

B 15 -> 20 -> 25 -> null

C 5 -> 10 -> 15 -> 20 -> 25 -> null

D 20 -> 25 -> null

💡 Hint

Each shift() removes one element from the front.

Two shift() calls remove 5 and then 10, leaving 15, 20, and 25.

❓ Predict Output

advanced

What error occurs if you try to delete the first element of a non-array?

What will happen when this code runs?

DSA Javascript

let notArray = 12345;
notArray.shift();

A TypeError: notArray.shift is not a function

B undefined

C 12345

D No output, code runs silently

💡 Hint

Only arrays have the shift() method.

Since notArray is a number, it does not have the shift() method, causing a TypeError.

🧠 Conceptual

expert

Why is deleting the first element of an array less efficient than deleting the last?

Choose the best explanation for why removing the first element of a JavaScript array is slower than removing the last element.

A Because shift() creates a new array internally every time it is called.

B Because deleting the first element requires sorting the array afterwards.

C Because arrays in JavaScript are linked lists and shifting requires traversal.

D Because shift() must move all other elements one position forward to fill the gap.

💡 Hint

Think about what happens to the indexes of elements after removing the first.

When shift() removes the first element, all remaining elements must be moved one index forward, which takes more time than removing the last element.

Practice

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

easy

A. Adds an element at the end

B. Removes the last element and returns it

C. Adds an element at the beginning

D. Removes the first element and returns it

Solution

1. Step 1: Understand the shift() method

   The shift() method removes the first element from an array and returns that element.

2. Step 2: Compare with other array methods

   pop() removes the last element, unshift() adds at the beginning, and push() adds at the end.

3. Final Answer:

   Removes the first element and returns it -> Option D

4. Quick Check:

   shift() removes first element [OK]

Hint: Remember: shift = remove from start [OK]

Common Mistakes:

• Confusing shift() with pop()
• Thinking shift() adds elements
• Mixing shift() with unshift()

2. Which of the following is the correct syntax to remove the first element from an array arr in JavaScript?

easy

A. arr.shift()

B. arr.delete(0)

C. arr.unshift()

D. arr.pop()

Solution

1. Step 1: Identify the method to remove first element

   The method to remove the first element is shift().

2. Step 2: Check other options

   pop() removes last element, unshift() adds elements at start, and delete is not a valid array method.

3. Final Answer:

   arr.shift() -> Option A

4. Quick Check:

   Use shift() to remove first element [OK]

Hint: Use arr.shift() to remove first element [OK]

Common Mistakes:

• Using pop() instead of shift()
• Trying to use delete() on arrays
• Confusing unshift() with shift()

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

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

medium

A. [20, 30, 40] and 10

B. [10, 20, 30] and 40

C. [20, 30, 40] and 40

D. [10, 20, 30] and 10

Solution

1. Step 1: Apply shift() on the array

   shift() removes the first element (10) from arr and returns it.

2. Step 2: Check the updated array and removed value

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

3. Final Answer:

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

4. Quick Check:

   shift() removes first element 10 [OK]

Hint: shift() returns removed first element [OK]

Common Mistakes:

• Expecting last element removed
• Confusing returned value with array
• Not updating array after shift()

4. Find the error in the following code that tries to remove the first element from array nums:

let nums = [5, 10, 15];
nums.remove(0);
console.log(nums);

medium

A. remove() removes last element, not first

B. remove() is not a valid array method

C. remove() requires two arguments

D. Code is correct and works fine

Solution

1. Step 1: Check the method used

   The method remove() does not exist for JavaScript arrays.

2. Step 2: Identify correct method to remove first element

   To remove the first element, use shift() instead of remove().

3. Final Answer:

   remove() is not a valid array method -> Option B

4. Quick Check:

   Use shift() to remove first element, not remove() [OK]

Hint: Use shift(), not remove(), to delete first element [OK]

Common Mistakes:

• Using remove() instead of shift()
• Assuming remove() exists in JS arrays
• Not checking method names carefully

5. Given an array data = [1, 2, 3, 4, 5], you want to remove the first two elements efficiently. Which code snippet correctly achieves this?

hard

A. data.shift(2);

B. data.pop(); data.pop();

C. data.splice(0, 2);

D. data.slice(2);

Solution

1. Step 1: Understand each method's effect

   shift(2) is invalid; shift() removes one element from start and takes no arguments. splice(0, 2) removes two elements starting at index 0 in one call. pop() removes from end, not start. slice(2) returns a new array without first two elements but does not modify original.

2. Step 2: Choose the best method to remove first two elements

   splice(0, 2) removes first two elements efficiently and modifies the original array.

3. Final Answer:

   data.splice(0, 2); -> Option C

4. Quick Check:

   splice(0, 2) removes first two elements [OK]

Hint: Use splice(0, 2) to remove first two elements at once [OK]

Common Mistakes:

• Using pop() which removes from end
• Using slice() which does not modify original array
• Using shift(2) which is invalid