JavaScript Data Types and Structures

Which of the following is a simple (primitive) data type in JavaScript?

• number

• array

• object

• function

Answer explanation

Correct Answer: number
❌ array → complex data type.
❌ object → complex data type.
❌ function → technically a type of object, not primitive.

True or False: Strings are considered complex data types.

• True
• False

Answer explanation

Correct Answer: False
❌ Strings are primitive data types.

What type of data structure is used to hold an ordered list of values?

• string

• array

• boolean

• number

Answer explanation

Correct Answer: array

❌ string → holds characters, not a list.
❌ boolean → only true/false.
❌ number → single numeric value.

Fill in the blank: Array indexes in JavaScript start at ____.

Answer explanation

Correct Answer: 0

• 10

• 20

• 30

• undefined

Answer explanation

Correct Answer: 20

❌ 10 → index 0.
❌ 30 → index 2.
❌ undefined → only happens if index doesn’t exist.

Which code correctly changes the second item in an array to 50?

• 
• 
• 
• 

Answer explanation

Correct Answer: nums[1] = 50;

❌ nums[2] = 50; → changes the third item.
❌ nums[0] = 50; → changes the first item.
❌ nums.update() → not valid in JS.

True or False: The .length property of an array returns the last index.

• True
• False

Answer explanation

Correct Answer: False

❌ .length returns the total count, not the last index.

• 2

• 3

• 4

• undefined

Answer explanation

Correct Answer: 3

Multi-select: Which methods can add a new item to an array?

• 
• 
• 
• 

Answer explanation

Correct Answers: .push(), .unshift()

❌ .shift() removes from the beginning.
❌ .pop() removes from the end.

Fill in the blank: nums.push(99) will add the number ____ to the end of the array.

Answer explanation

Correct Answer: 99