Array Insertion at Beginning in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a value at the beginning of the array.

DSA Typescript

let arr = [2, 3, 4];
arr.[1](1);
console.log(arr);

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

Apush

Bunshift

Cpop

Dshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using push instead of unshift, which adds at the end.

Using pop or shift which remove elements instead of adding.

The unshift method adds an element to the start of the array.

2fill in blank

medium

Complete the code to insert the number 0 at the beginning of the array.

DSA Typescript

const numbers = [1, 2, 3];
numbers.[1](0);
console.log(numbers);

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

Aunshift

Bpop

Cshift

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using push which adds at the end.

Using pop or shift which remove elements.

unshift adds the element at the start of the array.

3fill in blank

hard

Fix the error in the code to insert 'start' at the beginning of the array.

DSA Typescript

let items = ['middle', 'end'];
items.[1]('start');
console.log(items);

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

Aunshift

Bpush

Cpop

Dshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using push instead of unshift.

Using pop or shift which remove elements.

Use unshift to add an element at the beginning.

4fill in blank

hard

Fill both blanks to create an array with 0 at the beginning and 4 at the end.

DSA Typescript

let arr = [1, 2, 3];
arr.[1](0);
arr.[2](4);
console.log(arr);

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

Aunshift

Bpush

Cpop

Dshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using push to add at the start.

Using pop or shift which remove elements.

unshift adds at the start, push adds at the end.

5fill in blank

hard

Fill all three blanks to insert 'first' at start, remove last element, then add 'last' at end.

DSA Typescript

let list = ['middle'];
list.[1]('first');
list.[2]();
list.[3]('last');
console.log(list);

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

Aunshift

Bpop

Cpush

Dshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using shift instead of pop to remove last element.

Using push instead of unshift to add at start.

unshift adds at start, pop removes last, push adds at end.

Practice

1. What does inserting an element at the beginning of an array do to the existing elements?

easy

A. Replaces the first element with the new element

B. Deletes the last element of the array

C. Shifts all existing elements one position to the right

D. Leaves the array unchanged

Solution

1. Step 1: Understand array insertion at beginning

   When a new element is inserted at the start, all existing elements move one step to the right to make space.

2. Step 2: Effect on existing elements

   This shifting means the first element moves to second position, second to third, and so on.

3. Final Answer:

   Shifts all existing elements one position to the right -> Option C

4. Quick Check:

   Insert at start shifts elements right [OK]

Hint: New start element pushes others right [OK]

Common Mistakes:

• Thinking insertion replaces first element
• Assuming array size decreases
• Believing array stays unchanged

2. Which of the following is the correct TypeScript syntax to insert an element `5` at the beginning of array `arr`?

easy

A. arr.unshift(5);

B. arr.addFirst(5);

C. arr.insert(0, 5);

D. arr.push(5);

Solution

1. Step 1: Recall array methods for insertion

   In TypeScript (JavaScript), `unshift` adds elements at the start of an array.

2. Step 2: Check other options

   `push` adds at the end, `insert` and `addFirst` are not valid array methods.

3. Final Answer:

   arr.unshift(5); -> Option A

4. Quick Check:

   Use unshift() to add at beginning [OK]

Hint: Use unshift() to add at start [OK]

Common Mistakes:

• Using push() which adds at the end
• Using non-existent methods like insert()
• Confusing unshift() with pop()

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

let arr = [10, 20, 30];
arr.unshift(5);
console.log(arr);

medium

A. [10, 20, 30, 5]

B. [5, 10, 20, 30]

C. [5, 20, 30]

D. [10, 5, 20, 30]

Solution

1. Step 1: Understand unshift effect

   unshift(5) adds 5 at the start, shifting existing elements right.

2. Step 2: Resulting array

   Original [10, 20, 30] becomes [5, 10, 20, 30].

3. Final Answer:

   [5, 10, 20, 30] -> Option B

4. Quick Check:

   unshift adds at front [OK]

Hint: unshift adds element at front [OK]

Common Mistakes:

• Thinking unshift adds at end
• Misplacing the new element in the array
• Confusing unshift with push

4. Identify the error in the following TypeScript code that tries to insert `100` at the beginning of array `nums`.

let nums = [1, 2, 3];
nums.add(0, 100);
console.log(nums);

medium

A. `add` is not a valid method for arrays

B. `console.log` is used incorrectly

C. Array 'nums' is not declared properly

D. The element 100 cannot be added to arrays

Solution

1. Step 1: Check array method usage

   Arrays in TypeScript do not have an `add` method; insertion at beginning uses `unshift`.

2. Step 2: Validate other parts

   Declaration and console.log are correct; adding 100 is allowed.

3. Final Answer:

   `add` is not a valid method for arrays -> Option A

4. Quick Check:

   Use unshift(), not add() [OK]

Hint: Use unshift(), not add() for insertion [OK]

Common Mistakes:

• Using non-existent add() method
• Thinking console.log is wrong
• Believing arrays can't hold numbers

5. Given an empty array `let data: number[] = [];`, which sequence of operations will result in the array `[3, 2, 1]` by inserting elements only at the beginning?

hard

A. data.unshift(1); data.unshift(2); data.unshift(3);

B. data.push(1); data.push(2); data.push(3);

C. data.push(3); data.unshift(2); data.push(1);

D. data.unshift(3); data.unshift(2); data.unshift(1);

Solution

1. Step 1: Understand insertion at beginning

   Each unshift adds element at front, pushing existing elements right.

2. Step 2: Trace operations

   Starting empty: unshift(3) -> [3], unshift(2) -> [2,3], unshift(1) -> [1,2,3].

3. Final Answer:

   data.unshift(3); data.unshift(2); data.unshift(1); -> Option D

4. Quick Check:

   Insert in reverse order with unshift [OK]

Hint: Insert last element first with unshift [OK]

Common Mistakes:

• Using push() which adds at end
• Inserting elements in wrong order
• Mixing push and unshift incorrectly