JavaScript

Question 1

What is the purpose of variables?

Answer 1

To remember data for future reference.

Question 2

How do you declare a variable?

Answer 2

Write down keyword (var) to declare that variable.

Question 3

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

Answer 3

By using a single = sign, (= meaning assignment).

Question 4

What characters are allowed in variable names?

Answer 4

Letters, $, _ anywhere and numbers ,but number needs to be at the end.

Question 5

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

Answer 5

JavaScript does not consider lowercase and uppercase the same.

Question 6

What is the purpose of a string?

Answer 6

A way to hold a sequence of characters represented with letter characters.

Question 7

What is the purpose of a number?

Answer 7

To store numbers for calculation.

Question 8

What is the purpose of a boolean?

Answer 8

It allows us to render what is or isn’t.

Question 9

What does the = operator mean in JavaScript?

Answer 9

To assign a thing.

Question 10

How do you update the value of a variable?

Answer 10

No keyword is necessary.

Question 11

What is the difference between null and undefined?

Answer 11

Null can only be assigned and not generated by JavaScript, undefined comes from JavaScript.

Question 12

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

Answer 12

To know what you are looking at specifically.

Question 13

Give five examples of JavaScript primitives.

Answer 13

String, number, boolean, null, and undefined.

Question 14

What data type is returned by an arithmetic operation?

Answer 14

A number.

Question 15

What is string concatenation?

Answer 15

Any type of values being added to a string which results in one string.

Question 16

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

Answer 16

It can concatenate or be used for addition.

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

It adds the value to the variable and assigns that result to the variable.

Question 19

What are objects used for?

Answer 19

To group together a set of properties, variables and functions to give it grouping in one location.

Question 20

What are object properties?

Answer 20

The piece of data represented by the key and value.

Question 21

Describe object literal notation?

Answer 21

The data inside the {} for example: properties or key and values.

Question 22

How do you remove a property from an object?

Answer 22

With the delete operator and . name of the property

Question 23

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

Answer 23

You can use dot notation or bracket notation.

Question 24

What are arrays used for?

Answer 24

Good for rendering a list of data of any length and where the order is important or unimportant.

Question 25

Describe array literal notation.

Answer 25

Opening bracket and closing bracket with any number of data types inside the array.

Question 26

How are arrays different from "plain" objects?

Answer 26

All arrays have a length property while objects do not.

Question 27

What number represents the first index of an array?

Answer 27

Number 0.

Question 28

What is the length property of an array?

Answer 28

True count of how many items are in that array.

Question 29

How do you calculate the last index of an array?

Answer 29

Subtract 1 from the length property of an array.

Question 30

What is a function in JavaScript?

Answer 30

To group a series of statements together to preform a specific task.

Question 31

Describe the parts of a function definition.

Answer 31

Function, name for the function, parameters in a set of (), and a code block {}.

Question 32

Describe the parts of a function call.

Answer 32

Function name ().

Question 33

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

Answer 33

There is no code block in a call and the function keyword.

Question 34

What is the difference between a parameter and an argument?

Answer 34

Arguments are values provided when a function is called and parameter are values provided when a function is defined.

Question 35

Why are function parameters useful?

Answer 35

Parameters take in values and place them inside the function so that you can reuse the function instead of making multiple set of code for each value

Question 36

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

Answer 36

stops the function entirely and gives you a value to wherever the function is called

Question 37

Give 6 examples of comparison operators.

Answer 37

> (greater than), < (less than), >= (greater than or equal to), <= (less than or equal to), === (strictly equal), and !== (strictly not equal to)

Question 38

What data type do comparison expressions evaluate to?

Answer 38

boolean

Question 39

What is the purpose of an if statement?

Answer 39

It allows us to make a choice

Question 40

Is else required in order to use an if statement?

Answer 40

no it is not

Question 41

Describe the syntax (structure) of an if statement.

Answer 41

start with if then parenthesis and curly braces then your return statement inside then a else or else/if statement with a return

Question 42

What are the three logical operators?

Answer 42

&& (and), || (or), ! (not)

Question 43

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

Answer 43

using &&, or ||

Question 44

Why do we log things to the console?

Answer 44

to debug and see whats going on or to better understand what is happening

Question 45

What is a method?

Answer 45

function which is the value of an object stored

Question 46

How is a method different from any other function?

Answer 46

methods are attributed to an object and called by attaching a dot ( . ) to the object while function you can just call

Question 47

How do you remove the last element from an array?

Answer 47

by using the .pop method that goes off an array object

Question 48

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

Answer 48

the floor method takes it down to the nearest integer

Question 49

How do you generate a random number?

Answer 49

the random method for the object math

Question 50

How do you delete an element from an array?

Answer 50

the splice method for the array object with the argument index number to know where to delete from

Question 51

How do you append an element to an array?

Answer 51

the push method of the array object to add it to the end of an array

Question 52

How do you break a string up into an array?

Answer 52

the split method of the string with the argument string space (' ')

Question 53

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

Answer 53

it does not change the string and you can check by using the log method for the console object

Question 54

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

Answer 54

no

Question 55

What three-letter acronym should you always include in your Google search about a JavaScript method or CSS property?

Answer 55

mdn

Question 56

What is the purpose of a loop?

Answer 56

to repeat a block of code until a condition is no longer met

Question 57

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

Answer 57

the condition is there to stop the loop when it is not met

Question 58

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

Answer 58

one time the code block in the loop runs

Question 59

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

Answer 59

before each iteration

Question 60

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

Answer 60

from the beginning and just once

Question 61

When does the condition expression for a for loop get evaluated?

Answer 61

after the initialization and before each iteration of the code block

Question 62

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

Answer 62

at the end of each iteration, the final expression is what continues the loop

Question 63

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

Answer 63

break is how you escape a loop, break is used when you are looking for one value

Question 64

What does the ++ increment operator do?

Answer 64

increases the value by 1

Question 65

How do you iterate through the keys of an object?

Answer 65

using for in loop

Question 66

What is the event.target?

Answer 66

element you are interacting with

Question 67

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

Answer 67

makes element not visible, but still exists (no longer part of the flow or have no visual appearance)

Question 68

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

Answer 68

takes css selector and returns a boolean and whether the element matches the selector

Question 69

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

Answer 69

getAttribute(name of attribute) method

Question 70

At what steps of the solution would it be helpful to log things to the console?

Answer 70

every new line of code or expression

Question 71

If you were to add another tab and view to your HTML, but you didn't use event delegation, how would your JavaScript code be written instead?

Answer 71

you would have to have an individual conditional for each view and tab

Question 72

If you didn't use a loop to conditionally show or hide the views in the page, how would your JavaScript code be written instead?

Question 73

What is JSON?

Answer 73

text-based data format following JavaScript object syntax

Question 74

What are serialization and deserialization?

Answer 74

serialization is converting data into a stream of bytes and deserialization is the opposite

Question 75

Why are serialization and deserialization useful?

Answer 75

serialization sends data easily while deserialization converts back that data back to an object so that it is easy to work with

Question 76

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

Answer 76

JSON.stringify() method

Question 77

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

Answer 77

JSON.parce() method

Question 78

How do you store data in localStorage?

Answer 78

localStorage.setItem(name(keyName), value(keyValue)) method

Question 79

How do you retrieve data from localStorage?

Answer 79

localStorage.getItem(keyName) method

Question 80

What data type can localStorage save in the browser?

Answer 80

string data

Question 81

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

Answer 81

when the window, the document and its resources are about to be unloaded or when the page closes (close page, refresh page, or)

Question 82

In JavaScript, when is scope determined?

Answer 82

when it parses the code

Question 83

What allows JavaScript functions to "remember" values from their surroundings?

Answer 83

a closure

Question 84

What values does a closure contain?

Answer 84

all variables and functions within the closures parent scope

Question 85

When is a closure created?

Answer 85

everytime a function reference is created and captured at run time

Question 86

How can you tell if a function will be created as a closure?

Answer 86

if it needs any variables outside of itself

Question 87

In React, what is one important case where you need to know if a closure was created?