Array Insertion at End in DSA Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Array Insertion at End' mean?

It means adding a new item to the last position of an array, making the array longer by one.

beginner

Which JavaScript method is commonly used to insert an element at the end of an array?

The push() method adds one or more elements to the end of an array.

beginner

What happens to the array length after inserting an element at the end?

The array length increases by one for each element inserted at the end.

beginner

Show the result of this code:<br><code>let arr = [1, 2, 3]; arr.push(4);</code>

The array becomes [1, 2, 3, 4] after insertion at the end.

intermediate

Can you insert multiple elements at the end of an array at once using push()?

Yes, you can add multiple elements by passing them as arguments to push(), like arr.push(4, 5, 6).

Which method adds an element to the end of a JavaScript array?

A shift()

B pop()

C unshift()

D push()

push() adds elements to the end; pop() removes from the end; shift() removes from the start; unshift() adds to the start.

What is the length of array after this code?
let arr = [5, 6]; arr.push(7);

A 1

B 2

C 3

D 4

Original length is 2; after pushing one element, length becomes 3.

What will be the output of this code?
let arr = []; arr.push('a'); arr.push('b');

A ['b']

B ['a', 'b']

C ['a']

D []

Each push adds an element at the end, so array becomes ['a', 'b'].

Which of these is NOT true about push()?

A It adds elements at the start of the array

B It returns the new length of the array

C It can add multiple elements at once

D It changes the original array

push() adds elements at the end, not the start.

If arr = [1, 2, 3], what does arr.push(4, 5) do?

A Adds 4 and 5 at the end

B Adds 4 only

C Adds 5 only

D Throws an error

push() can add multiple elements; here 4 and 5 are added at the end.

Explain how to insert an element at the end of an array in JavaScript and what happens to the array length.

Think about the method that changes the array size by adding at the end.

Describe what happens when you use push() with multiple arguments on an array.

Remember that push can take more than one element.

Practice

1. What does the push() method do when used on a JavaScript array?

easy

A. Adds one or more elements to the end of the array

B. Removes the first element from the array

C. Sorts the array in ascending order

D. Reverses the order of elements in the array

Solution

1. Step 1: Understand the purpose of push()

   The push() method is designed to add elements to the end of an array.

2. Step 2: Compare with other array methods

   Other methods like shift() remove elements, sort() orders elements, and reverse() changes order, but push() only adds at the end.

3. Final Answer:

   Adds one or more elements to the end of the array -> Option A

4. Quick Check:

   push() adds elements at end [OK]

Hint: Remember: push adds at the end, pop removes from end [OK]

Common Mistakes:

• Confusing push() with pop() which removes elements
• Thinking push() adds elements at the start
• Mixing push() with sort() or reverse()

2. Which of the following is the correct syntax to add the element 5 at the end of array arr?

easy

A. arr.add(5);

B. arr.append(5);

C. arr.insertEnd(5);

D. arr.push(5);

Solution

1. Step 1: Recall JavaScript array methods

   JavaScript arrays use push() to add elements at the end.

2. Step 2: Check each option's validity

   add(), insertEnd(), and append() are not valid JavaScript array methods.

3. Final Answer:

   arr.push(5); -> Option D

4. Quick Check:

   Correct syntax for adding at end is push() [OK]

Hint: Use push() to add elements at array end [OK]

Common Mistakes:

• Using non-existent methods like add() or append()
• Confusing push() with unshift() which adds at start
• Missing parentheses in method call

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

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

medium

A. [1, 2, 3]

B. [4, 1, 2, 3]

C. [1, 2, 3, 4]

D. Error

Solution

1. Step 1: Understand initial array and push operation

   The array starts as [1, 2, 3]. The push(4) adds 4 at the end.

2. Step 2: Determine final array content

   After push, the array becomes [1, 2, 3, 4].

3. Final Answer:

   [1, 2, 3, 4] -> Option C

4. Quick Check:

   push(4) adds 4 at end [OK]

Hint: push() adds element at end, so array grows rightwards [OK]

Common Mistakes:

• Thinking push adds element at start
• Expecting original array unchanged
• Confusing push with unshift

4. Identify the error in the following code snippet that tries to add 10 at the end of array nums:

let nums = [1, 2, 3];
nums.push = 10;
console.log(nums);

medium

A. Using assignment instead of calling push as a function

B. Array nums is not defined

C. push method does not exist on arrays

D. Missing semicolon after push

Solution

1. Step 1: Analyze the push usage

   The code assigns 10 to nums.push instead of calling nums.push(10).

2. Step 2: Understand consequences of assignment

   This overwrites the push method with a number, so push no longer works as a function.

3. Final Answer:

   Using assignment instead of calling push as a function -> Option A

4. Quick Check:

   push must be called as a function, not assigned [OK]

Hint: Always call push() with parentheses to add elements [OK]

Common Mistakes:

• Assigning value to push instead of calling it
• Forgetting parentheses after push
• Assuming push is a property, not a method

5. Given the code below, what will be the final state of arr?

let arr = [10];
arr.push(20);
arr.push(30, 40);
arr.push();

hard

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

B. [10, 20, 30, 40]

C. [10, 20, 30, 40, undefined]

D. [10, 20, 30]

Solution

1. Step 1: Trace each push call

   Initial array: [10]. arr.push(20) adds 20 -> [10, 20]. arr.push(30, 40) adds both 30 and 40 -> [10, 20, 30, 40]. arr.push() with no arguments adds nothing.

2. Step 2: Confirm final array state

   No undefined or nested arrays are added. Final array is [10, 20, 30, 40].

3. Final Answer:

   [10, 20, 30, 40] -> Option B

4. Quick Check:

   push() adds all args at end; no args means no change [OK]

Hint: push() adds all arguments; no args means no change [OK]

Common Mistakes:

• Thinking push() with no args adds undefined
• Assuming push(30, 40) adds an array instead of separate elements
• Confusing nested arrays with multiple arguments