JavaScript

Question 1

What is the purpose of variables?

Answer 1

To temporarily store data needed to run scripts

Question 2

How do you “declare” a variable?

Answer 2

Using the keyword var
var variableName = variableValue

Question 3

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

Answer 3

= (assignment operator)

Question 4

What characters are allowed in variable names?

Answer 4

Letters, $, _

Question 5

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

Answer 5

Uppercases matter: tom is different than Tom

Question 6

What is the purpose of a string?

Answer 6

To assign any text value

Question 7

What is the purpose of a number?

Answer 7

Used for counting / calculating

Question 8

What is the purpose of a boolean?

Answer 8

Gives true or false, helps determine which script to run

Question 9

What does the |=| operator mean in JavaScript?

Answer 9

Assignment operator

Question 10

How do you update the value of a variable?

Answer 10

variableName = newValue

Question 11

What is the difference between |null| and |undefined|?

Answer 11

Null represents an invalid or nonexistent object, undefined represents no value

Question 12

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

Answer 12

To help with debugging and know which functions you are working with

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 operative?

Answer 14

Number

Question 15

What is string concatenation?

Answer 15

Combining strings and numbers together for a longer string

Question 16

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

Answer 16

Concatenation and adding values

Question 17

What data type is returned by comparing two values?

Answer 17

Booleans

Question 18

What does the |+=| “plus-equals” serve in JavaScript?

Answer 18

Adds value of the right side to a variable and assigns result to said variable

Question 19

What are objects used for?

Answer 19

To create a model of something recognizable from the real world by grouping together a set of variables and functions

Question 20

What are object properties?

Answer 20

Variables that are part of the object

Question 21

Describe object literal notation.

Answer 21

var objectName = {
key: value, };

Question 22

How do you remove a property from an object?

Answer 22

delete objectName.propertyName;

Question 23

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

Answer 23

dot notation or square brackets

Question 24

What are arrays used for?

Answer 24

When you are working with a list or set of values related to each other.

Question 25

Describe array literal notation.

Answer 25

var arrayName = ['string', value, ..., 'string'];

Question 26

How are arrays different from "plain" objects?

Answer 26

Arrays use index numbers for the key for each value.

Question 27

What number represents the first index of an array?

Answer 27

Zero

Question 28

What is the |length| property of an array?

Answer 28

arrayName.length

Question 29

How do you calculate the last index of an array?

Answer 29

arrayName.length - 1

Question 30

What is a function in JavaScript?

Answer 30

Written code to be used throughout the program.

Question 31

Describe the parts of a function |definition|.

Answer 31

function functionName (parameters) { code block return;}

Question 32

Describe the parts of a function |call|.

Answer 32

functionName (argument);

Question 33

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

Answer 33

Defining has the |function| keyword

Question 34

What is the difference between a |parameter| and an |argument|?

Answer 34

Parameters are placeholders, arguments are the actual values to be passed through the function.

Question 35

Why are function |parameters| useful?

Answer 35

They allow the function to have any value.

Question 36

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

Answer 36

Causes the function to produce a value, prevents anymore code in the function code block from being run

Question 37

Why do we log things to the console?

Answer 37

To check if our output is correct and to see the data

Question 38

What is a method?

Answer 38

A function which is a property of an object

Question 39

How is a method different from any other function?

Answer 39

Methods are already defined / associated with objects.

Question 40

How do you remove the last element from an array?

Answer 40

arrayName.pop()

Question 41

How do you round a number down to the nearest integer?

Answer 41

Math.floor()

Question 42

How do you generate a random number?

Answer 42

Math.random()

Question 43

How do you delete an element from an array?

Answer 43

splice() -> splice (start, delete count)

Question 44

How do you append an element to an array?

Answer 44

push() - to the end of array unshift() - to the front of array

Question 45

How do you break a string up into an array?

Answer 45

split(), pass argument to divide

Question 46

Do string methods change the original string? How would you check if you weren't sure?

Answer 46

No the string stays the same, the output is different. With console.log

Question 47

Roughly how many string methods are there according to the MDN docs?

Answer 47

Roughly 50

Question 48

Is the return value of a function or method useful in every situation?

Answer 48

Not every situation

Question 49

Roughly how may array methods are there according to MDN?

Answer 49

Roughly 40

Question 50

Give 6 examples of comparison operators?

Answer 50

==, !=, ===, !==, >, >=, <, <=

Question 51

What data type do comparison expressions evaluate to?

Answer 51

Booleans: true / false

Question 52

Is |else| required in order to use an |if| statement?

Answer 52

No

Question 53

Describe the syntax (structure) of an |if| statement?

Answer 53

if (condition) {code block}

Question 54

What is the purpose of a loop?

Answer 54

To run code multiple times on it's own

Question 55

What is the purpose of a "condition" expression in a loop?

Answer 55

To tell the code to continue running or to stop

Question 56

What does "iteration" mean in the context of the loop?

Answer 56

The number of times the loop has run

Question 57

When does the "condition" expression of a |while| loop get evaluated?

Answer 57

Before executing the statement

Question 58

When does the "initialization" expression of a |for| loop get evaluated?

Answer 58

Before the first loop starts

Question 59

When does the "condition" expression of a |for| loop get evaluated?

Answer 59

In every iteration of the loop

Question 60

When does the "final" expression of a |for| loop get evaluated?

Answer 60

After the code block is run

Question 61

Besides a |return| statement, which exits its entire function block, which keyword exits a loop before it's "condition" expression evaluates to |false|?

Answer 61

Break

Question 62

What does the |++| increment operator do?

Answer 62

Adds 1 to the counter

Question 63

What event is fired when a user places their cursor in a form control?

Answer 63

focus

Question 64

What event is fired when a user's cursor leaves a form control?

Answer 64

blur

Question 65

What event is fired when a user changes the value of a form control?

Answer 65

input

Question 66

What event is fired when a user clicks the |"submit"| button within a |

|?

Answer 66

submit

Question 67

What does the |event.preventDefault()| method do?

Answer 67

Blocks an event from doing the "default"

Question 68

What does submitting a form without |event.preventDefault()| do?

Answer 68

Automatically reloading the page with values stored in the URL.

Question 69

What property of a form element object contains all of the form's controls?

Answer 69

Elements property

Question 70

What property of a form control objects gets and sets its value?

Answer 70

objectName.elements.elementName.value