JavaScript Data Types (Booleans, Objects, Arrays)

Question 1

What is a JavaScript boolean?

Answer 1

A data type representing a truth value: true or false.

Question 2

Give an example of a use case for booleans.

Answer 2

Conditional logic (e.g., if statements), flags/switches, comparisons in loops.

Question 3

How do you declare a boolean variable in JavaScript?

Answer 3

let isLoggedIn = true; or let isAdult = false.

Question 4

What are the ‘falsy’ values in JavaScript?

Answer 4

0, “” (empty string), null, undefined, NaN.

Question 5

What is a JavaScript object?

Answer 5

A collection of properties, where each property has a key (name) and a value.

Question 6

Give an example of a use case for objects.

Answer 6

Representing real-world entities (users, products), storing configurations, organizing code.

Question 7

How do you create an object in JavaScript?

Answer 7

Using curly braces {}: let person = { name: “Alice”, age: 30 };

Question 8

How do you access a property in an object using dot notation?

Answer 8

objectName.propertyName (e.g., person.name).

Question 9

How do you access a property in an object using bracket notation?

Answer 9

objectName[“propertyName”] (e.g., person[“age”]) - Useful for variable keys.

Question 10

What is a method in an object?

Answer 10

A function defined as a property of an object. It can be called using object.methodName().

Question 11

What does this refer to inside an object’s method?

Answer 11

The object itself.

Question 12

How do you add a new property to an existing object?

Answer 12

objectName.newProperty = value.

Question 13

How do you delete a property from an object?

Answer 13

delete objectName.propertyName.

Question 14

What is a JavaScript array?

Answer 14

An ordered list of values.

Question 15

Give an example of a use case for arrays.

Answer 15

Storing lists of items, representing collections of data, performing operations on sequences.

Question 16

How do you create an array in JavaScript?

Answer 16

Using square brackets []: let colors = [“red”, “green”, “blue”];

Question 17

How do you access an element in an array?

Answer 17

Using its index (starting from 0): arrayName[index] (e.g., colors[0]).

Question 18

How do you find the number of elements in an array?

Answer 18

Using the length property: arrayName.length.

Question 19

Name three common array methods for adding/removing elements.

Answer 19

push() (add to end), pop() (remove from end), shift() (remove from beginning), unshift() (add to beginning).

Question 20

Explain the difference between slice() and splice() array methods.

Answer 20

slice() creates a new array containing a portion of the original. splice() modifies the original array by removing or replacing elements.