Accessing array elements in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Accessing nested array elements

What is the output of the following code?

Javascript

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

A [2, 3]

B 3

C undefined

D 2

💡 Hint

Remember that arr[1] is an array itself, so you need to access its elements by index.

arr[1] is the array [2, 3]. Accessing arr[1][0] gets the first element of that inner array, which is 2.

❓ Predict Output

intermediate

Accessing array elements with negative index

What will be the output of this code?

Javascript

const arr = [10, 20, 30];
console.log(arr[-1]);

A 30

B -1

C undefined

D SyntaxError

💡 Hint

JavaScript arrays do not support negative indices like some other languages.

In JavaScript, negative indices do not access elements from the end. arr[-1] is undefined because no property '-1' exists.

❓ Predict Output

advanced

Accessing array elements after modification

What is the output of this code?

Javascript

const arr = [5, 10, 15];
arr[5] = 25;
console.log(arr.length);
console.log(arr[3]);

A

6
undefined

B

3
undefined

C

6
0

D

5
undefined

💡 Hint

Setting an element at index 5 changes the length of the array.

Assigning arr[5] = 25 sets the sixth element (index 5), so length becomes 6. arr[3] was never set, so it is undefined.

❓ Predict Output

advanced

Accessing array elements with destructuring

What will be logged by this code?

Javascript

const arr = [100, 200, 300];
const [a, , c] = arr;
console.log(a, c);

A 100 300

B 100 200

C 200 300

D undefined undefined

💡 Hint

Destructuring skips the second element with the empty comma.

The destructuring assigns a = arr[0] = 100, skips arr[1], and assigns c = arr[2] = 300.

❓ Predict Output

expert

Accessing array elements with dynamic keys

What is the output of this code?

Javascript

const arr = [1, 2, 3];
const key = '1';
console.log(arr[key]);

A undefined

B 2

C 1

D TypeError

💡 Hint

Array indices are converted to strings internally.

JavaScript arrays use string keys for indices. arr['1'] accesses the element at index 1, which is 2.