Javascript

Question 1

What is the purpose of variables

Answer 1

To store data that you assign to it

Question 2

How do you declare a variable?

Answer 2

Var

Question 3

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

Answer 3

Using the assignment operator of =

Question 4

What characters are allowed in variable name?

Answer 4

Name must begin with a letter, dollar sign, or underscore. CANNOT begin with a number.

Question 5

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

Answer 5

That if a variable has the same name as another variable by one is capitalized, they are not considered the same

Question 6

What is the purpose of a string?

Answer 6

To add text

Question 7

What is the purpose of a number?

Answer 7

For task that involve counting or calculating sums

Question 8

What is the purpose of a boolean?

Answer 8

Helpful when determining what steps are required next depending on what conditions are met

Question 9

What does the = operator mean in Javascript?

Answer 9

The variable’s values is being assigned to the variable’s name

Question 10

How do you update the value of a variable?

Answer 10

Once you have declared that variable with the var keyword and assigned it a variable name and value, you only need to call the variable name and assign it a new value

Question 11

What is the difference between null and undefined?

Answer 11

Undefined means that a value was never assigned to the variable and null is essentially a placeholder for a value created by the developer. In null you can place values in, in undefined you cannot.

Question 12

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

Answer 12

It helps you from getting confused when logging; it is a short string that describes the variable being logged

Question 13

Give five examples of JavaScript primitives

Answer 13

String, number, boolean, undefined, and null

Question 14

What data type is returned by an arithmetic operation?

Answer 14

Numbers

Question 15

What is string concatenation?

Answer 15

When you combine strings together

Question 16

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

Answer 16

To perform arithmetic operations or to concatenate strings

Question 17

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

Answer 17

Boolean

Question 18

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

Answer 18

Adds a value to an existing variable and assigns the new value back to the same variable

Question 19

What are objects used for?

Answer 19

They are used to group together a set of variables and methods

Question 20

What are object properties?

Answer 20

Variables with a name and value

Question 21

Describe object literal notation

Answer 21

IT is an array of (key:value) pairs that are are placed inside of curly brackets

Question 22

How do you remove a property from an object?

Answer 22

by using the delete method nameofObject.property

Question 23

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

Answer 23

Using period notation or square brackets

Question 24

What are arrays used for?

Answer 24

To store a list of values

Question 25

Describe array literal notation

Answer 25

You define a new array with empty square brackets

Question 26

How are arrays different from "plain" objects?

Answer 26

Array are index objects are not

Question 27

What kind of data types are array?

Answer 27

Reference data types

Question 28

What is a function in JavaScript?

Answer 28

A set of statements that perform a task or calculates a value It should take some input and return an output

Question 29

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

Answer 29

When you call a function you are only using the name of the function and the parameter you want to put in it

Question 30

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

Answer 30

Stops the function from running. Returns the function being called

Question 31

What is the difference if you declare a variable outside vs inside a function?

Answer 31

* If a variable is being defined within a function you can only use it in the function o If it is declared outside of the function that is fine because you can just give the function a new value in the function

Question 32

Why do we log things to the console?

Answer 32

To constantly be informed on what our code is doing

Question 33

what is a method?

Answer 33

Actions that can be performed on objects

Question 34

How is a method different from any other function?

Answer 34

A method is associated with an object, while a function is not A method is passed on the object it is called on

Question 35

How do you remove the last element from an array?

Answer 35

Using the pop() method

Question 36

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

Answer 36

Math.floor()

Question 37

How do you generate a random number?

Answer 37

o Math.random()

Question 38

How do you delete an element from an array?

Answer 38

splice

Question 39

How do you append an element to an array?

Answer 39

By using .push() or shift()

Question 40

How do you break a string up into an array?

Answer 40

By using split

Question 41

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

Answer 41

No they are not able to change

Question 42

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

Answer 42

No because you might not want it returned

Question 43

Give 6 examples of comparison operators.

Answer 43

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

Question 44

What data type do comparison expressions evaluate to?

Answer 44

Boolean to see if it is true or false

Question 45

What is the purpose of an if statement?

Answer 45

To guide a program to make decisions based on specific criteria

Question 46

Is else required in order to use an if statement?

Answer 46

It is not required you can just write if statements

Question 47

Describe the syntax (structure) of an if statement.

Answer 47

If (condition) { two sets of code for different outcomes}

Question 48

What are the three logical operators?

Answer 48

&&, ||, and !

Question 49

How do you compare two different expressions in the same condition?

Answer 49

By using &&, ||

Question 50

What is the purpose of a loop?

Answer 50

Repeats a sequence of instructions until a specific condition is met

Question 51

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

Answer 51

It test the condition each time the loop repeats

Question 52

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

Answer 52

At the beginning of each iteration

Question 53

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

Answer 53

The very start of the loop

Question 54

When does the condition expression of a for loop get evaluated

Answer 54

It after the initialization and before every iteration

Question 55

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

Answer 55

At the end of the iteration

Question 56

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

Answer 56

break

Question 57

How do you iterate through the keys of an object?

Answer 57

For ... in loop

Question 58

What are the four components of "the Cascade".

Answer 58

Source code, inheritance, specificity, and !important

Question 59

What does the term "source order" mean with respect to CSS?

Answer 59

The order that your CSS rules are written in your stylesheet

Question 60

How is it possible for the styles of an element to be applied to its children as well without an additional CSS rule?

Answer 60

Inherited properties which by default are set to the computed value of the parent element

Question 61

List the three selector types in order of increasing specificity.

Answer 61

No value, type, class, id

Question 62

Why is using !important considered bad practice?

Answer 62

It makes it difficult for other people to go in and make changes because they’ll have to be aware of what you put important on. It disrupts the natural flow in applying the css rules where properties are applied from top to bottom.

Question 63

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

Answer 63

The ‘focus’ event

Question 64

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

Answer 64

the 'blur' event

Question 65

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

Answer 65

The ‘input’ event

Question 66

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

?

Answer 66

The ‘submit’ event

Question 67

What does the event.preventDefault() method do?

Answer 67

o Cancels the event if it is cancelable, meaning that the default action that belongs to the event will not occur o Will allow us to submit manually o Prevents the default behavior

Question 68

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

Answer 68

o The request that you inputted is submitting the form the request to the URL o You might want to do more things to the data before actually sending a request

Question 69

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

Answer 69

o The “elements” property o .elements

Question 70

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

Answer 70

.value

Question 71

What is one risk of writing a lot of code without checking to see if it works so far?

Answer 71

If you do not catch the errors early one then the validity of the code after that mistake is in question

Question 72

What is an advantage of having your console open when writing a JavaScript program?

Answer 72

You can console log anything you wish to check into the console

Question 73

What is the event.target?

Answer 73

Whatever element that we are interacting with

Question 74

What is the affect of setting an element to display: none?

Answer 74

Removes whatever element that we currently on the screen

Question 75

What does the element.matches() method take as an argument and what does it return?

Answer 75

Matches compares the attribute as an argument with the attribute of whatever element you are comparing it to

Question 76

How can you retrieve the value of an element's attribute?

Answer 76

o .getAttribute()

Question 77

What is JSON?

Answer 77

It is a text based format for representing structured data based on Javascript object syntax

Question 78

What are serialization and deserialization?

Answer 78

o Serialization is the process of turning an object in memory into a stream of bytes so you can send it over the network  Turning it into a string o Deserialization is the reverse process of turning a stream of bytes into an object in memory  Back into an object

Question 79

Why are serialization and deserialization useful?

Answer 79

o Gives us a way to transmit data across different devices o Clean way of being able to transmit data

Question 80

How do you serialize a data structure into a JSON string using JavaScript?

Answer 80

o JSON.stringify()

Question 81

How do you deserialize a JSON string into a data structure using JavaScript?

Answer 81

o JSON.parse()

Question 82

How do you store data in localStorage?

Answer 82

localStorage.setItem(keyName, KeyValue)

Question 83

How do you retrieve data from localStorage?

Answer 83

localStorage.getItem() pass in the keyName and it should return the value or null if the key does not exist

Question 84

What data type can localStorage save in the browser?

Answer 84

JSON string

Question 85

When does the 'beforeunload' event fire on the window object?

Answer 85

Before the page gets reloaded