JavaScript Basics

Question 1

What is the purpose of variables?

Answer 1

To store and re-use data

Question 2

How do you declare a variable?

Answer 2

Using the var, const, or let keyword followed by the name of the variable

Question 3

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

Answer 3

Using the var, const, or let keyword followed by the name of the variable followed by an assignment operator followed by a value

Question 4

What characters are allowed in variable names?

Answer 4

Letters, numbers, period, underscore, dollar sign

The first character of a variable name cannot be a number

Question 5

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

Answer 5

You can only use the exact matching name of a variable as a value for anything

Question 6

What is the purpose of a string?

Answer 6

Allows you to create strings of characters

Question 7

What is the purpose of a number?

Answer 7

It allows you to hold numeric value and perform calculations

Question 8

What is the purpose of a boolean?

Answer 8

To use True or False values, such as conditionals

Question 9

What does the = operator mean in JavaScript?

Answer 9

It’s the assignment operator

Question 10

How do you update the value of a variable?

Answer 10

Without declaring the variable, assign the variable a new value

Question 11

What is the difference between null and undefined?

Answer 11

Undefined means a value does not exist

Null is an assigned value that was used intentionally

Question 12

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

Answer 12

It makes debugging easier when you know the value of what variable the console.log is returning

Question 13

Give five examples of JavaScript primitives

Answer 13

String, number, boolean, null, undefined

Question 14

What data type is returned by an arithmetic operation?

Answer 14

Numeric value

Question 15

What is string concatenation?

Answer 15

Combining two or more string values

Question 16

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

Answer 16

It either adds numbers or concatenates strings

Question 17

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

Answer 17

Boolean, True or False

Question 18

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

Answer 18

It adds (or concatenates) the current variable and a value, then assigns the result to the variable

Question 19

What are objects used for?

Answer 19

Objects group together a set of variables and functions to create a model of something you would recognize from the real world

Question 20

What ar eobject properties?

Answer 20

Object properties are variables

Properties can be functions, referred to as Methods

Question 21

Describe object literal notation

Answer 21

An object is a set of opening and closing curly braces and their content, known as key value pairs

Key value pairs need to be separated by a colon, and end in a comma (Unless it’s the last key value pair of the object)

Question 22

How do you remove a property from an object?

Answer 22

Using the delete operator before the dot notation or bracket notation for the object.property

Question 23

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

Answer 23

Using dot notation or bracket notation for the object property

To update, use the assignment operator before the new value

Question 24

What are arrays used for?

Answer 24

To hold related value as a list

Question 25

Describe array literal notation

Answer 25

Square brackets containing items

items are separated by a comma unless it’s the last index of the array

Question 26

How are arrays different from “plain” objects?

Answer 26

Arrays can be indexed numerically

To get or update a value in the array, you have to use a numerical index

Question 27

What number represents the first index of an array?

Answer 27

0

Question 28

What is the length property of an array?

Answer 28

The length property returns the total number of values in an array

Question 29

How do you calculate the last index of an array?

Answer 29

array.length - 1

Question 30

What is a function in JavaScript?

Answer 30

A block of reusable code that we can use as needed

Question 31

Describe the parts of a function definition

Answer 31

Using the function keyword followed by an optional name and a pair of parentheses, which contains optional parameters

After the parentheses, you have a pair of curly braces for the definition block

Question 32

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

Answer 32

A function call will not have the function keyword nor a pair of curly braces for the definition block

Question 33

Describe the parts of a function call

Answer 33

You call a function by using the functions name followed by a set of parentheses to pass arguments

Question 34

What is the difference between a parameter and an argument?

Answer 34

A parameter is a placeholder for arguments while defining the definition

An argument is a value being passed while calling the definition

Question 35

Why are function parameters useful?

Answer 35

Parameters allow you to store data and use their value in the definition block to return a result

Question 36

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

Answer 36

A return will return a value and it will break the function, not allowing any code after the return value to execute