JavaScript

Question 1

What is the purpose of variables?

Answer 1

The purpose of variables is to store a value.

Question 2

How do you declare a variable?

Answer 2

A variable is declared with the const, var, or let keyword along with a name. e.g. ‘var test’.

Question 3

How do you initialize (assign a value to) a variable?

Answer 3

To initialize a variable you use the = operator. e.g. ‘var test = ‘test’ ‘.

Question 4

What characters are allowed in variable names?

Answer 4

The characters used must be a letter, underscore, or $.

Question 5

What does it mean to say that variable names are “case sensitive”?

Answer 5

Variables are distinguished by their capitalization. e.g. ‘var Test’ and var test’ are different variables.

Question 6

What is the purpose of a string?

Answer 6

A string is used to store a sequence of characters.

Question 7

What is the purpose of a number?

Answer 7

A number is used to store numeric values.

Question 8

What is the purpose of a boolean?

Answer 8

A boolean is used to store a true/false value.

Question 9

What does the = operator mean in JavaScript?

Answer 9

The = operator is the assignment operator. It assign a value to a variable.

Question 10

How do you update the value of a variable?

Answer 10

To update a variable you call the variable along with a new value. e.g. ‘test = ‘hi’.

Question 11

What is the difference between null and undefined?

Answer 11

The Null type is purposely defined, while undefined is typically accidental.

Question 12

Why is it a good habit to include “labels” when you log values to the browser console?

Answer 12

Adding labels to console log makes it easier to distinguish where the value is coming from.

Question 13

Give five examples of JavaScript primitives.

Answer 13

The JavaScript primitives are: Number, String, Boolean, undefined, BigInt, and Symbol.

Question 14

What data type is returned by an arithmetic operation?

Answer 14

Numeric data is returned by an arithmetic operation.

Question 15

What is string concatenation?

Answer 15

String concatenation is joining strings by using the + operator. e.g. ‘var test = ‘hi ‘ + ‘name’ will return ‘hi name’.

Question 16

What purpose(s) does the + plus operator serve in JavaScript?

Answer 16

The + operator is used for concatenation along with addition.

Question 17

What data type is returned by comparing two values (, ===, etc)?

Answer 17

The data type returned by comparison operators is a boolean. e.g. true/false

Question 18

What does the += “plus-equals” operator do?

Answer 18

The += operator adds both sides of an assignment together before assigning. e.g. var test = 1, var hello = 1
test += hello is now equal to '2'.

Question 19

What are objects used for?

Answer 19

Objects are used to store multiple values.

Question 20

What are object properties?

Answer 20

Object properties are the names of their values. e.g. ‘number: 2’.

Question 21

Describe object literal notation.

Answer 21

A variable declaration followed by an object literal its containing properties, that are separated by commas, and a closing literal. e.g. var object = { property: ‘value’ }

Question 22

How do you remove a property from an object?

Answer 22

To remove a property from an object the ‘delete’ operator would be used. e.g. ‘delete object.property’.

Question 23

What are the two ways to get or update the value of a property?

Answer 23

To get/update a property you can use either bracket or dot notation. e.g. object.property or object[‘property’].

Question 24

What are arrays used for?

Answer 24

Arrays are used to store multiple values.

Question 25

Describe array literal notation.

Answer 25

A variable declaration followed by an array literal its containing properties, that are separated by commas, and a closing literal. e.g. var array = [ ‘value’ ]

Question 26

How are arrays different from “plain” objects?

Answer 26

Arrays store multiple values without property names.

Question 27

What number represents the first index of an array?

Answer 27

The first index of an array is [0]. The first value is stored in ‘0’ not ‘1’.

Question 28

What is the length property of an array?

Answer 28

The length property is the number of values stored within the array.

Question 29

How do you calculate the last index of an array?

Answer 29

To find the last index of an array you would use ‘array.length - 1’ as the index starts with 0 not 1.

Question 30

What is a function in JavaScript?

Answer 30

A function is a code block designed for a certain task that can be repeatedly used with different inputs.

Question 31

Describe the parts of a function definition.

Answer 31

A function definition consists of the function keyword followed by an optional name, a comma separated list of zero or more parameters surrounded by parentheses, the opening code block using ‘{‘, an optional return statement, and the ending block ‘}’.

Question 32

Describe the parts of a function call.

Answer 32

A function call consists of the function’s name and arguments to input.

Question 33

When comparing them side-by-side, what are the differences between a function call and a function definition?

Answer 33

A function definition needs the function keyword and placeholder parameter names. A function call needs just the function name and the input rather than parameters.

Question 34

What is the difference between a parameter and an argument?

Answer 34

A Parameter is a placeholder for a value. An argument is that said value.

Question 35

Why are function parameters useful?

Answer 35

Parameters allow easy access to the inputted value via its name.

Question 36

What two effects does a return statement have on the behavior of a function?

Answer 36

A return statement will exit the code block and not continue while also outputting a value.