JavaScript

Question 1

What is the purpose of variables?

Answer 1

hold on to data for the future

Question 2

How do you declare a variable?

Answer 2

var (var is the keyword)

Question 3

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

Answer 3

=

Question 4

What characters are allowed in variable names?

Answer 4

The name must begin with
a letter, dollar sign ($),or an
underscore (_). It must not start
with a number. You cannot use keywords or reserved words.

Question 5

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

Answer 5

All variables are case sensitive,
so score and Score would be
different variable names, but
it is bad practice to create two
variables that have the same
name using different cases.

Question 6

What is the purpose of a string?

Answer 6

hold a sequence of characters

Question 7

What is the purpose of a number?

Answer 7

store numbers for calculations

Question 8

What is the purpose of a boolean?

Answer 8

Booleans are helpful when
determining which part of a
script should run.

“make a choice”

Question 9

What does the = operator mean in JavaScript?

Answer 9

assignment

Question 10

How do you update the value of a variable?

Answer 10

You just use the
variable name, the equals sign
(also known as the assignment
operator), and the new value for
that attribute.

Question 11

What is the difference between null and undefined?

Answer 11

null= can only be assigned (is/was actually assigned on purpose) 1. i’ll get data later 2. i’ll never get it but need to show you

undefined is a primitive value automatically assigned to variables that have just been declared, or to formal arguments for which there are no actual arguments. (javascript says “i never received it”

Question 12

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

Answer 12

if you do not include “labels”, it can be very confusing instead of helpful. A console log “label” is simply a short string that describes the variable or value being logged.

Since the console.log() method can write multiple values to the console at the same time, it’s easy to include a “label” when printing a value.

Question 13

Give five examples of JavaScript primitives.

Answer 13

string.
number.
bigint.
boolean.
undefined.
symbol.
null.

Question 14

console.log(‘value of fullName:’, fullName);

Answer 14

log method of the console object is being called with 2 arguments, the string ‘value of fullname’ and the variable fullName.

Question 15

var fullName = ‘Cody Miller’

Answer 15

string cody miller is being assigned to the variable fullName

Question 16

console.log(‘typeof fullName:’, typeof fullName);

Answer 16

log method of the console object is being called with 2 arguments, the string typeof full name and th result of typeof fullname

Question 17

var never;

Answer 17

variable never is being declared but never assigned a value

Question 18

What data type is returned by an arithmetic operation?

Answer 18

basic math

Question 19

What is string concatenation?

Answer 19

two or more strings to create 1 string

Question 20

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

Answer 20

adds one value to another and concatenate

Question 21

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

Answer 21

boolean

Question 22

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

Answer 22

adds

Question 23

motto += ‘ is the GOAT”

Answer 23

the value of the variable motto is being concatenated with the string ‘ is the goat’ and the result is being assigned to the variable motto

Question 24

What are objects used for?

Answer 24

Objects group together a set of variables and functions to create a model of a something

Question 25

What are object properties?

Answer 25

IN AN OBJECT: VARIABLES BECOME KNOWN AS PROPERTIES

Question 26

Describe object literal notation.

Answer 26

object stored in a variable (optional), content separates each key from its value inside curly braces

Question 27

How do you remove a property from an object?

Answer 27

delete

Question 28

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

Answer 28

dot notation hotel.name = 'park'; bracket notation hotel['name'] = 'park'

Question 29

var student = { firstname: Luke lastname: skywalker age: 25 };

Answer 29

object literal assigned to variable student string luke assigned to variable firstname

Question 30

code reading

Answer 30

. === "of" [] === at

Question 31

right of . left of .

Answer 31

property object

Question 32

What are arrays used for?

Answer 32

whenever you are working with a list or a set of values that are related to each other. Arrays are especially helpful when you do not know how many items a list will contain where order is either important or not important

Question 33

Describe array literal notation.

Answer 33

The values are assigned to the array inside a pair of square brackets, and each value is separated by a comma. The values in the array do not need to be the same data type, so you can store a string, a number and a Boolean all in the same array.

Question 34

How are arrays different from "plain" objects?

Answer 34

object = order of properties not important array= index numbers dictate order of properties, has length

Question 35

What number represents the first index of an array?

Answer 35

0

Question 36

What is the length property of an array?

Answer 36

how many items in the array

Question 37

How do you calculate the last index of an array?

Answer 37

.length -1

Question 38

What is a function in JavaScript?

Answer 38

Functions let you group a series of statements together to perform a specific task. If different parts of a script repeat the same task, you can reuse the function (rather than repeating the same set of statements).

Question 39

Describe the parts of a function definition.

Answer 39

1. The function keyword to begin the creation of a new function. 2. An optional name. (Our function's name is sayHello.) 3. A comma-separated list of zero or more parameters, surrounded by () parentheses. (Our sayHello function doesn't have any parameters.) 4. The start of the function's code block, as indicated by an { opening curly brace. 5. An optional return statement. (Our sayHello function doesn't have a return statement.) 6. The end of the function's code block, as indicated by a } closing curly brace.

Question 40

Describe the parts of a function call.

Answer 40

once defined - can be called (code within its code block to run) write name of function with (parameters) next to it - this causes code block within function's definition to be executed

Question 41

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

Answer 41

parameters for definition / arguments for calling; function keyword

Question 42

What is the difference between a parameter and an argument?

Answer 42

You can think of a parameter as a placeholder. It is basically a variable whose value is not known until we call the function and pass an argument. When the function's code block is run, the parameter is will be holding the value of the argument.

Question 43

Why are function parameters useful?

Answer 43

gives u a process to use for values many times

Question 44

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

Answer 44

1. Causes the function to produce a value we can use in our program. 2. Prevents any more code in the function's code block from being run.

Question 45

function code reading

Answer 45

function definition named convert with one parameter minutes with opening curly brace for code block value of variable minutes multiply by 60 and result is assigned to variable seconds value of variable seconds is being returned from the function convertmnitestoseconds is being called with one parameter and the result is being returned to the variable ______.

Question 46

Why do we log things to the console?

Answer 46

The JavaScript console is a debugging tool. It is where the browser prints errors and warnings as they occur in your JavaScript code.

Question 47

What is a method?

Answer 47

A JavaScript method is a property of an object that contains a function definition. Methods are functions stored as object properties

Question 48

How is a method different from any other function?

Answer 48

Methods are functions stored as object properties. The difference is that a method is associated with an object, while a function is not.

Question 49

How do you remove the last element from an array?

Answer 49

pop() method

Question 50

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

Answer 50

Math.floor() function

Question 51

How do you generate a random number?

Answer 51

Math. random()

Question 52

How do you delete an element from an array?

Answer 52

splice()

Question 53

How do you append an element to an array?

Answer 53

push()

Question 54

How do you break a string up into an array?

Answer 54

split()

Question 55

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

Answer 55

no, console.log in javascript, strings cannot be changed ever

Question 56

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

Answer 56

no

Question 57

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

Answer 57

mdn

Question 58

Give 6 examples of comparison operators.

Question 59

What data type do comparison expressions evaluate to?

Question 60

What is the purpose of an if statement?

Question 61

Is else required in order to use an if statement?

Question 62

Describe the syntax (structure) of an if statement.

Question 63

What are the three logical operators?

Question 64

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

Question 65

What is the purpose of a loop?

Answer 65

repeat a code block until specified condition is no longer met

Question 66

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

Answer 66

run until the counter reaches a specified number (brakes)

Question 67

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

Answer 67

one time a full loop runs

Question 68

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

Answer 68

before each iteration

Question 69

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

Answer 69

first time the loop is run (initialization = "before anything)

Question 70

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

Answer 70

after initialization - after each iteration of code block until counter reaches a specified number

Question 71

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

Answer 71

after each iteration (the is the gas/accelerator)

Question 72

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

Answer 72

break;

Question 73

What does the ++ increment operator do?

Answer 73

increment by 1

Question 74

How do you iterate through the keys of an object?

Answer 74

arr[i].keyname

Question 75

What is JSON?

Answer 75

JSON is an extremely common data interchange format used to send and store information in computer systems. Before JSON, XML was a popular data interchange format, but JSON's simplicity and readability has made it the preferred format.

Question 76

What are serialization and deserialization?

Answer 76

Serialization is a process of converting an Object into stream of bytes so that it can be transferred over a network or stored in a persistent storage. Deserialization is the exact opposite - Fetch a stream of bytes from network or persistence storage and convert it back to the Object with the same state.

Question 77

Why are serialization and deserialization useful?

Answer 77

The purpose of serializing it into JSON is so that the message will be a format that can be understood and from there, deserialize it into an object type that makes sense for the consumer.

Question 78

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

Answer 78

JSON.stringify()

Question 79

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

Answer 79

JSON.parse()

Question 80

How do you store data in localStorage?

Answer 80

The setItem() method of the Storage interface, when passed a key name and value, will add that key to the given Storage object, or update that key's value if it already exists.

Question 81

How do you retrieve data from localStorage?

Answer 81

The getItem() method of the Storage interface, when passed a key name, will return that key's value, or null if the key does not exist, in the given Storage object.

Question 82

What data type can localStorage save in the browser?

Answer 82

strings

Question 83

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

Answer 83

The beforeunload event is fired when the window, the document and its resources are about to be unloaded. The document is still visible and the event is still cancelable at this point.

Question 84

if local storage acts wonky

Answer 84

shift / out the before unload event, delete local storage, refresh, and unshift out the before unload event

Question 85

Closures

Answer 85

Think of a closure as a container or a box. The outer function is like the container or the box, and the inner function is like an object that's stored inside the container or the box. When the outer function is executed, it creates the container or the box, and the inner function is stored inside it. Now, imagine that the inner function needs to access some variables that are outside of the container or the box. Normally, when the outer function is finished executing and the container or the box is closed, those variables would no longer be accessible. However, because the inner function is still inside the container or the box, it has access to those variables, even though they're outside of the container or the box. So, just like how an object stored inside a container or a box has access to other objects stored inside the same container or box, an inner function stored inside an outer function has access to variables defined in the outer function. I hope this analogy helps make closures in JavaScript a bit easier to understand!