JavaScript Fundamentals

Question 1

What was JavaScript initially called?

Answer 1

LiveScript

Question 2

What is the specification for JavaScript?

Answer 2

ECMAScript

Question 3

True or False: JavaScript and Java are the same.

Answer 3

False

Question 4

List three benefits of using JavaScript.

Answer 4

• Full integration with HTML/CSS
• Simple things are done simply
• Support by all major browsers and enabled by default

Question 5

What is the primary task of a JavaScript engine?

Answer 5

To convert (compile) the JavaScript to machine-executable binaries.

Question 6

What are two examples of JavaScript engines?

Answer 6

• V8 (Chrome, Opera, Edge)
• SpiderMonkey (Firefox)

Question 7

What is the basic structure of JavaScript code?

Answer 7

JavaScript commands are written in statements separated by semicolons.

Question 8

What are the keywords used to declare a variable in JavaScript?

Answer 8

• const
• var
• let

Question 9

What characters are allowed in variable names?

Answer 9

• Letters
• Digits
• Symbols $ and _

Question 10

What is the special value that represents nothing in JavaScript?

Answer 10

null

Question 11

What does the Boolean type represent?

Answer 11

Two values: true and false.

Question 12

What is the maximum safe integer value in JavaScript?

Answer 12

2**53 - 1 (9,007,199,254,740,991) - just over 9 quadrillion

Question 13

Fill in the blank: In JavaScript, a _______ is a special value that indicates a variable has been declared but not assigned a value.

Answer 13

undefined

Question 14

What is the syntax to create a string with embedded expressions?

Answer 14

Backticks (``)

Question 15

True or False: All data types in JavaScript are considered primitive except for objects.

Answer 15

True

Question 16

What operator is used to check the type of a variable?

Answer 16

typeof

Question 17

What is the result of typeof null?

Answer 17

object

Question 18

What is the purpose of the String class function in type conversion?

Answer 18

To explicitly convert other types to strings.

Question 19

What happens during implicit numeric conversion in JavaScript?

Answer 19

Strings are automatically converted to numbers in mathematical operations.

Question 20

List three values that convert to false in Boolean conversion.

Answer 20

• ””
• 0
• null

Question 21

What does a variable declared but not assigned a value return when logged?

Answer 21

undefined

Question 22

How can you create a BigInt in JavaScript?

Answer 22

By appending ‘n’ to an integer.

Question 23

What is a key characteristic of JavaScript as a programming language?

Answer 23

JavaScript is a dynamically typed language.

Question 24

What is the output of console.log(NaN ? ‘NaN is true’ : ‘NaN is false’)?

Answer 24

NaN is false

Question 25

What is the output of console.log(0 ? 'zero is true' : 'zero is false')?

Answer 25

zero is false

Question 26

What is the output of console.log('hello' ? 'hello is true' : 'hello is false')?

Answer 26

hello is true

Question 27

What does the negation operator (!) do?

Answer 27

Converts a value to boolean and then negates it

Question 28

What is the output of console.log(!undefined)?

Answer 28

true

Question 29

What is the output of console.log(!!"" )?

Answer 29

false

Question 30

How does JavaScript compare strings?

Answer 30

Using dictionary or lexicographical order

Question 31

What is the first step in comparing two strings?

Answer 31

Compare the first character of both strings

Question 32

If both strings have the same first character, what should be done next?

Answer 32

Compare the second characters the same way

Question 33

What is the output of console.log('apple' < 'banana')?

Answer 33

true

Question 34

What happens when comparing different types using >, <, == and !=?

Answer 34

JavaScript converts the values to numbers

Question 35

What is the output of console.log('2' > 1)?

Answer 35

true

Question 36

What does the 'return' keyword do in a function?

Answer 36

Sends a value back to where the function was called

Question 37

What is the syntax for a function declaration?

Answer 37

function functionName(parameters) { // function body }

Question 38

What is the purpose of the DRY principle in programming?

Answer 38

Avoiding repetition by defining code once and calling it multiple times

Question 39

What is the difference between function declaration and function expression?

Answer 39

Function declaration can be hoisted; function expression cannot be accessed before definition

Question 40

What is an arrow function?

Answer 40

A concise version of function expression using => syntax

Question 41

How do arrow functions differ from regular functions in terms of 'arguments'?

Answer 41

Arrow functions cannot access the 'arguments' variable

Question 42

What is an object in JavaScript?

Answer 42

A complex variable that stores keyed collections of various data

Question 43

How can an object be created in JavaScript?

Answer 43

Using curly brackets {} or the Object constructor

Question 44

What is a property in an object?

Answer 44

A key:value pair where key is a string and value can be anything

Question 45

What happens when accessing a non-existing property of an object?

Answer 45

It returns undefined

Question 46

How can you iterate over all keys of an object?

Answer 46

Using a for ... in loop

Question 47

What is the output of console.log(object) if object = { 2: 'value of numeric property', '2': 'value of string property' }?

Answer 47

{ '2': 'value of string property' }

Question 48

What is the difference between shallow copy and deep clone?

Answer 48

Shallow copy replicates the structure but not nested object properties; deep clone copies all levels

Question 49

What is a method in the context of an object?

Answer 49

A function that is a property of an object

Question 50

How can an object method access its own properties?

Answer 50

Using the 'this' keyword

Question 51

What keyword is used to access the information stored in an object within its methods?

Answer 51

this

Question 52

In the context of an object method, what does the value of 'this' refer to?

Answer 52

The object before the dot, the one used to call the method.

Question 53

What is the output of user.printGreeting() when user is defined as { name: 'Bilbo Baggins', printGreeting() { console.log(`Hello, I'm ${this.name}`) } }?

Answer 53

Hello, I'm Bilbo Baggins

Question 54

True or False: The value of 'this' in JavaScript is evaluated at compile-time.

Answer 54

False

Question 55

What allows methods to be chained together in JavaScript objects?

Answer 55

Returning 'this' from a method.

Question 56

What are the naming conventions for constructor functions in JavaScript?

Answer 56

Named with a capital letter first.

Question 57

What must be used to execute a constructor function?

Answer 57

The new operator.

Question 58

What is the first step when a function is executed with the 'new' keyword?

Answer 58

A new empty object is created and assigned to 'this'.

Question 59

What is one difference between constructor functions and ES6 classes?

Answer 59

Classes have an explicit constructor function.

Question 60

Fill in the blank: In ES6, the new syntax keyword _______ is introduced for creating object blueprints.

Answer 60

class

Question 61

What does the hasShortName method return for a user with first name 'Tim'?

Answer 61

true

Question 62

List three advantages of programming in JavaScript.

Answer 62

* Event-driven * Asynchronous * High-level

Question 63

What are the three keywords used to create a variable in JavaScript?

Answer 63

* var * let * const

Question 64

What are five common variable data types in JavaScript?

Answer 64

* Number * String * Boolean * Object * Undefined

Question 65

What are the three types of quotes used to create a string in JavaScript?

Answer 65

* Single quotes * Double quotes * Backticks

Question 66

What is the difference between null and undefined?

Answer 66

Null is an intentional absence of value; undefined means a variable has been declared but not assigned.

Question 67

How can we convert a variable to a string in JavaScript?

Answer 67

Using String() or .toString() method.

Question 68

How can we convert a variable to a number in JavaScript?

Answer 68

Using Number() or parseInt()/parseFloat() methods.

Question 69

What is a boolean?

Answer 69

A data type that can be either true or false.

Question 70

What are the three ways to create a function in JavaScript?

Answer 70

* Function declaration * Function expression * Arrow function

Question 71

What is an object in JavaScript?

Answer 71

A collection of properties, each defined as a key-value pair.

Question 72

How can we create an object in JavaScript?

Answer 72

Using object literal syntax or constructor functions.