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LearningFuze > JavaScript > Flashcards

JavaScript Flashcards

1
Q

Why do we log things to the console?

A

to see the state of the code
tracking values, debugging

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2
Q

What is a “model”?

A

a recreation of something for resemblance

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3
Q

Which “document” is being referred to in the phrase Document Object Model?

A

HTML document

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4
Q

What is the word “object” referring to in the phrase Document Object Model?

A

javascript object

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5
Q

What is a DOM Tree?

A

element and all of its content

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6
Q

Give two examples of document methods that retrieve a single element from the DOM.

A

queryselector and getelementbyid

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7
Q

Give one example of a document method that retrieves multiple elements from the DOM at once.

A

queryselectorall

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8
Q

Why might you want to assign the return value of a DOM query to a variable?

A

to be able to reuse it later
so you don’t have to do the same work

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9
Q

Why would a script tag need to be placed at the bottom of the HTML content instead of at the top?

A

so the html and css finishes loading

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10
Q

What console method allows you to inspect the properties of a DOM element object?

A

console.dir

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11
Q

What does document.querySelector() take as its argument and what does it return?

A

css selector and it returns first element of that selector

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12
Q

What does document.querySelectorAll() take as its argument and what does it return?

A

css selector and a nodelist with all elements with that selector

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13
Q

Why do we log things to the console?

A

to verify values and debug

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14
Q

What is the purpose of events and event handling?

A

events are for detecting user interaction and response

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15
Q

Are all possible parameters required to use a JavaScript method or function?

A

no

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16
Q

What method of element objects lets you set up a function to be called when a specific type of event occurs?

A

addeventlistener

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17
Q

What is a callback function?

A

function that gets called when something else happens

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18
Q

What object is passed into an event listener callback when the event fires?

A

callback function

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19
Q

What is the event.target? If you weren’t sure, how would you check? Where could you get more information about it?

A

event target is to see which event triggered. if you didn’t know, you could look it up on mdn

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20
Q

What is the className property of element objects?

A

get or set value of class attribute on html element

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21
Q

How do you update the CSS class attribute of an element using JavaScript?

A

classname property of object equal operator to value

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22
Q

What is the textContent property of element objects?

A

text that is being displayed

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23
Q

Is the event parameter of an event listener callback always useful?

A

no

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24
Q

Would this assignment be simpler or more complicated if we didn’t use a variable to keep track of the number of clicks?

A

more complicated

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25
Q

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

A

focus event

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26
Q

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

A

blur event

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27
Q

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

A

value event

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28
Q

What event is fired when a user clicks the “submit” button within a ?

A

submit event

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29
Q

What does the event.preventDefault() method do?

A

prevent someone from doing the default behavior of event

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30
Q

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

A

refreshes the page

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31
Q

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

A

elements

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32
Q

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

A

value

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33
Q

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

A

it could break along the way

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34
Q

Does the document.createElement() method insert a new element into the page?

A

no

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35
Q

How do you add an element as a child to another element?

A

appendchild method

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36
Q

What do you pass as the arguments to the element.setAttribute() method?

A

first argument would be the attribute you want, the second would be the value

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37
Q

What steps do you need to take in order to insert a new element into the page?

A

appendchild to an element inside the page already

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38
Q

What is the textContent property of an element object for?

A

get value or reassign text

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39
Q

Name two ways to set the class attribute of a DOM element.

A

property classname, and assign it a value, or use setattribute method

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40
Q

What are two advantages of defining a function to do create something (like the work of creating a DOM tree)?

A

function is reusable and the return can be used somewhere else

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41
Q

Give two examples of media features that you can query in an @media rule.

A

min-width and min-height

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42
Q

What is the event.target?

A

the origin of the element that got triggered

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43
Q

Why is it possible to listen for events on one element that actually happen its descendent elements?

A

event bubbling

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44
Q

What DOM element property tells you what type of element it is?

A

tagName

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45
Q

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

A

css selector and returns closest parent element

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46
Q

How can you remove an element from the DOM?

A

remove method

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47
Q

What is the event.target?

A

the origin element that got triggered

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48
Q

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

A

takes it out of view and document flow

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49
Q

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

A

takes css selector as argument and return boolean depending on if the targeted element matches the css selector

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50
Q

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

A

getattribute method

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51
Q

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

A

anytime u need it

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52
Q

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?

A

need an event listener for each tab

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53
Q

What is a breakpoint in responsive Web design?

A

the point where the layout/ website changes to adjust for devices

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54
Q

What is the advantage of using a percentage (e.g. 50%) width instead of a fixed (e.g. px) width for a “column” class in a responsive layout?

A

adaptability and less possible failure points

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55
Q

What is JSON?

A

way to store long term data by converting data into strings

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56
Q

What are serialization and deserialization?

A

serialization is to convert human data for humans into data for the computer. deserialization is to convert computer data into readable human data.

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57
Q

Why are serialization and deserialization useful?

A

to store and transfer data in an efficient way.

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58
Q

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

A

stringify method of JSON object or type it out

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59
Q

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

A

parse method of JSON object

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60
Q

How do you store data in localStorage?

A

setItem method

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61
Q

How do you retrieve data from localStorage?

A

getItem method, keyname as argument

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62
Q

What data type can localStorage save in the browser?

A

a string

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63
Q

When does the ‘beforeunload’ event fire on the window object?

A

when the tab is refreshed or closed

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64
Q

What is a method?

A

function being stored in property of an object

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65
Q

How can you tell the difference between a method definition and a method call?

A

if a method is being defined the word function will be prevalent. if it is being called only the function name followed by parentheses will be present.

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66
Q

Describe method definition syntax (structure).

A

object name, dot, method name, followed by parentheses and argument.

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67
Q

Describe method call syntax (structure).

A

object name, dot, function name, paranthesis

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68
Q

How is a method different from any other function?

A

you have to specify object name before with a dot

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69
Q

What is the defining characteristic of Object-Oriented Programming?

A

pairing data with behavior in the same space

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70
Q

What are the four “principles” of Object-Oriented Programming?

A

abstraction, encapsulation, inheritance, polymorphism

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71
Q

What is “abstraction”?

A

take a complex tool and give a simple interface for it

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72
Q

What does API stand for?

A

Application programming interface

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73
Q

What is the purpose of an API?

A

allow people to use complex tools without fully understanding/creating them

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74
Q

What is this in JavaScript?

A

gets the value of whatever is being used

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75
Q

What does it mean to say that this is an “implicit parameter”?

A

implied that it’s there, no visual queues to be seen

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76
Q

When is the value of this determined in a function; call time or definition time?

A

call time

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77
Q

What does this refer to in the following code snippet?

A

nothing

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78
Q

What kind of inheritance does the JavaScript programming language use?

A

prototype based programming

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79
Q

What is a prototype in JavaScript?

A

an object with methods you can use on the main variable

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80
Q

How is it possible to call methods on strings, arrays, and numbers even though those methods don’t actually exist on strings, arrays, and numbers?

A

prototype

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81
Q

If an object does not have it’s own property or method by a given key, where does JavaScript look for it?

A

prototype of said data

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82
Q

What does the new operator do?

A

creates a new data set based on the function called

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83
Q

What property of JavaScript functions can store shared behavior for instances created with new?

A

prototype

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84
Q

What does the instanceof operator do?

A

It checks to see if it has the prototype/methods of an object

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85
Q

What is a “callback” function?

A

function that gets executed later

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86
Q

Besides adding an event listener callback function to an element or the document, what is one way to delay the execution of a JavaScript function until some point in the future?

A

setTimeout

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87
Q

How can you set up a function to be called repeatedly without using a loop?

A

setInterval

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88
Q

What is the default time delay if you omit the delay parameter from setTimeout() or setInterval()?

A

0

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89
Q

What do setTimeout() and setInterval() return?

A

the interval ID

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90
Q

What is AJAX?

A

sending information, receiving information and updating without refreshing the site.

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91
Q

What does the AJAX acronym stand for?

A

Asynchronous JavaScript And XML

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92
Q

Which object is built into the browser for making HTTP requests in JavaScript?

A

XML http request

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93
Q

What event is fired by XMLHttpRequest objects when they are finished loading the data from the server?

A

load event

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94
Q

An XMLHttpRequest object has an addEventListener() method just like DOM elements. How is it possible that they both share this functionality?

A

XHR shares prototype with dom elements.

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95
Q

What is a code block? What are some examples of a code block?

A

curly braces

96
Q

What does block scope mean?

A

area of where the variable exists inside a block

97
Q

What is the scope of a variable declared with const or let?

A

block

98
Q

What is the scope of a variable declared with var

A

block, var variables are function scoped

99
Q

What is the difference between let and const?

A

let can be reassigned

100
Q

Why is it possible to .push() a new value into a const variable that points to an Array?

A

value of content is mutable, but not reassignable

101
Q

How should you decide on which type of declaration to use?

A

use const until you cant

102
Q

What is the syntax for writing a template literal?

A

string ${variable}

103
Q

What is “string interpolation”?

A

substitute string with variables

104
Q

What is destructuring, conceptually?

A

getting property values/array elements and assigning them into multiple variables in one line

105
Q

syntax for object destructuring

A

let {property: variableName} = object

106
Q

syntax for array destructuring

A

let [a, b, c] = array

107
Q

How can you tell the difference between destructuring and creating object/array literals

A

where the brackets are located, left is destructuring, while creating is on the right of the assignment operator

108
Q

What is the syntax for defining an arrow function?

A

parameter, equals greater than, then code block

109
Q

What is the syntax for defining an arrow function?

A

parameter, equals greater than, then code block or return expression

110
Q

When an arrow function’s body is left without curly braces, what changes in its functionality?

A

implicit return for statement (return expression)

111
Q

How is the value of this determined within an arrow function?

A

it shadows the outer function

112
Q

What is a CLI?

A

command line interface

113
Q

What is a GUI?

A

graphical user interface

114
Q

Give at least one use case for each of the commands listed in this exercise.
man
cat
ls
pwd
echo
touch
mkdir
mv
rm
cp

A

man - manual
cat - see content
ls - list items in a directory
pwd - print directory
echo - create text
touch - create file/ change time
mkdir - make folder/directory
mv - rename/move directory
rm - remove files/directories
cp - copy

115
Q

What are the three virtues of a great programmer?

A

laziness, impatient, humorous

116
Q

What is Node.js?

A

way to run javascript outside a web browser

117
Q

What can Node.js be used for?

A

backend for web apps, command line programs

118
Q

What is a REPL?

A

read–eval–print loop
takes input, executes actions, returns product to the user

119
Q

When was NodeJS created?

A

May 27, 2009

120
Q

What back end languages have you heard of?

A

ruby, python, java, rust, javascript, php, c++, golang, c, c#

121
Q

What is the process object in a Node.js program?

A

global variable that stores data about entire program

122
Q

How do you access the process object in a Node.js program?

A

you can just reference it like any other variable

123
Q

What is the data type of process.argv in Node.js?

A

array of strings

124
Q

What is a JavaScript module?

A

a new js file, containing code of a smaller component out of a bigger codebase

125
Q

What values are passed into a Node.js module’s local scope?

A

filename, dirname, module, exports, require

126
Q

Give two examples of truly global variables in a Node.js program.

A

process and console

127
Q

What is the purpose of module.exports in a Node.js module?

A

to be able to use a value from that module

128
Q

How do you import functionality into a Node.js module from another Node.js module?

A

require function

129
Q

What is the process object in a Node.js program?

A

global variable with all of the information about current process

130
Q

How do you access the process object in a Node.js program?

A

reference process, because it is global

131
Q

What is the data type of process.argv in Node.js?

A

array

132
Q

What is a JavaScript module?

A

another js file containing a small part of code

133
Q

What values are passed into a Node.js module’s local scope?

A

export, module, require, __filename, __dirname

134
Q

Give two examples of truly global variables in a Node.js program.

A

global & process

135
Q

What is the purpose of module.exports in a Node.js module?

A

get a value from a module to be able to use into others

136
Q

How do you import functionality into a Node.js module from another Node.js module?

A

require function

137
Q

What is the JavaScript Event Loop?

A

responsible for taking callbacks from stack and putting them in a queue

138
Q

What is a directory?

A

folder

139
Q

what is a relative file path

A

specifies path from current spot

140
Q

what is an absolute file path

A

specifies path from root directory

141
Q

What method is available in the Node.js fs module for writing data to a file?

A

writeFile

142
Q

What is a client?

A

computer that sends a request to a server

143
Q

What is a server?

A

computer that respond to requesters with information

144
Q

Which HTTP method does a browser issue to a web server when you visit a URL?

A

GET request

145
Q

What is on the first line of an HTTP request message?

A

HTTP method, request target, protocol version

146
Q

What is on the first line of an HTTP response message?

A

protocol, status code, and text for status

147
Q

What are HTTP headers?

A

extra meta information

148
Q

Is a body required for a valid HTTP message?

A

no

149
Q

What is NPM?

A

node package manager

150
Q

What is a package?

A

pre made reusable code (package.json, directory, one or more files)

151
Q

How can you create a package.json with npm?

A

npm init –yes

152
Q

What is a dependency and how to you add one to a package?

A

third party code that you can use

153
Q

How do you add express to your package dependencies?

A

npm install express

154
Q

How do you add express to your package dependencies?

A

npm install express

155
Q

How do you mount a middleware with an Express application?

A

use method to the app object, and callback function will be an argument. cb will be middleware

156
Q

What is the appropriate Content-Type header for HTTP messages that contain JSON in their bodies?

A

applications/json

156
Q

What is the significance of an HTTP request’s method?

A

allows the programmer to know what function to do

157
Q

What is a database schema?

A

how database is stored

158
Q

What is a table?

A

collection of rows where every row has attribute

159
Q

What is a row?

A

each specific item

160
Q

What is PostgreSQL and what are some alternative relational databases?

A

postgresql is a relational database, an alternative to relational database is monodb which uses json

161
Q

What are some advantages of learning a relational database?

A

efficiency and organizing

162
Q

What does the express.json() middleware do and when would you need it?

A

parses JSON body of request, and you would need it anytime you want to change data

163
Q

What is SQL and how is it different from languages like JavaScript?

A

in SQL we state what we want and we get it, while in JS we declare things and get create the result by ourselves

164
Q

How do you retrieve specific columns from a database table?

A

select keyword then column names separated by commas

165
Q

How do you filter rows based on some specific criteria?

A

where clause

166
Q

What are the benefits of formatting your SQL?

A

organizing

167
Q

How do you limit the number of rows returned in a result set?

A

limit keyword

168
Q

What are four comparison operators that can be used in a where clause?

A

=, !=, <, >

169
Q

How do you retrieve all columns from a database table?

A

*

170
Q

How do you control the sort order of a result set?

A

order by keyword

171
Q

What is a tuple?

A

a row

172
Q

How do you get back the row being inserted into a table without a separate select statement?

A

returning

173
Q

How do you add a row to a SQL table?

A

insert value, them tuple

174
Q

How do you add multiple rows to a SQL table at once?

A

multiple tupiles

175
Q

How do you specific update rows in a database table?

A

set what you want with a where clause

176
Q

Why is it important to include a where clause in your update statements?

A

you will update everything that meets that condition

177
Q

How do you delete rows from a database table?

A

delete from “table”

178
Q

what is a foreign key?

A

shared data value

179
Q

How do you join two SQL tables?

A

join keyword followed by table name in quotes, followed by using keyword and foreign key in quotes in paranthesis

180
Q

How do you temporarily rename columns or tables in a SQL statement?

A

as keyword - you can use it on columns and tables

181
Q

What are some examples of aggregate functions?

A

sum, count, max

182
Q

What is the purpose of a group by clause?

A

separate rows into groups

183
Q

what are the 3 states a promise can be in

A

pending, fulfilled, and rejected

184
Q

How do you handle the fulfillment of a Promise?

A

.then method

185
Q

How do you handle the rejection of a Promise?

A
186
Q

What is Array.prototype.filter useful for?

A

get specific elements for an array

187
Q

what is webpack

A

create a bundle out of modules

188
Q

How do you add a devDependency to a package?

A

–save-dev

189
Q

what is an npm script

A

automate npm commands

190
Q

how do u execute webpack with npm run

A

npm run (key)

191
Q

What is “syntactic sugar”?

A

write code in a readable way

192
Q

What is the typeof an ES6 class?

A

function

193
Q

Describe ES6 class syntax.

A

function name, brackets, then constructor, parameter, brackets, then methods name, parameter, brackets

194
Q

What is “refactoring”?

A

rewriting code to improve it without affecting functionality

195
Q

How are ES Modules different from CommonJS modules?

A

syntax, es6 modules are async, es6 modules are official

196
Q

what is react

A

frontend framework

197
Q

What is a React element?

A

object

198
Q

How do you mount a React element to the DOM?

A

grab a real root element, make it a react root, set a react element, and mount the element to the root by using render method

199
Q

what is babel

A

compiler to convert different versions of js to more compatible versions

200
Q

what is a plugin

A

additional software on pre existing software

201
Q

what is a webpack loader

A

transformations that are applied to the source code of a module

202
Q

how can you make babel and webpack work together

A

use babel loader in webpack

203
Q

what is jsx?

A

javascript syntax extension

204
Q

why must the react object be imported when authoring jsx in a module

A

jsx compiles into react

205
Q

how can you make webpack and babel work together to convert jsx into valid JavaScript

A

we use babel loader plugins to convert into valid JS and webpack takes all of modules & packages & bundles them

206
Q

What is a React component?

A

function that returns react elements

207
Q

How do you define a function component in React?

A

regular function definition with capital first letter as name, and parameter props

208
Q

How do you mount a component to the DOM?

A

call render method of root object passing component as argument

209
Q

library vs framework

A

ioc (inversion of control)
library - code that you call
framework - calls your code, you give ur power to framework

210
Q

what are props in react

A

object that contains properties

211
Q

How do you pass props to a component?

A

prop name equals value, if it is an expression it has to be wrapped in curly braces

212
Q

How do you create “class” component in React?

A

define class but extends to React.Component and need atleast one prototype method that is render, and that render returns react element

213
Q

what is the purpose of state in react

A

data model of values that changes overtime

214
Q

What are controlled components?

A

inputs values is owned by state of component

215
Q

What two props must you pass to an input for it to be “controlled”?

A

value and onChange

216
Q

What Array method is commonly used to create a list of React elements?

A

.map

217
Q

What does express.static() return?

A

a function

218
Q

What is the local __dirname variable in a Node.js module?

A

path to the current directory

219
Q

What does the join() method of Node’s path module do?

A

combines strings to form a path

220
Q

what does fetch() return

A

promise

221
Q

what is the default request method used by fetch()

A

get

222
Q

When does React call a component’s componentDidMount method?

A

after the first render

223
Q

Name three React.Component lifecycle methods.

A

constructor, render, componentdidmount

224
Q

How do you pass data to a child component?

A

props

225
Q

what does a LIFO mean?

A

last in first out

226
Q

What methods are available on a Stack data structure?

A

pop and push

227
Q

What must you do to access the value at an arbitrary point in a stack (not just the “top”)?

A

you have to pop until you reach that point

228
Q

What must you do to access the value at an arbitrary point in a stack (not just the “top”)?

A

you have to pop until you reach that point

229
Q

What does the acronym FIFO mean?

A

first in first out

230
Q

What methods are available on a Queue data structure?

A

enqueue and dequeue

231
Q

What must you do to access the value at an arbitrary point in a queue (not just the “front”)?

A

get rid of the ones before

232
Q

how are linked lists different from an array

A

in an array u can go to a random index while in a linked list its linear

233
Q

how would u access an arbitrary node in a linked list (not just the “head”)?

A

to get to an arbitrary node in a linkedlist u have to go through everything before it

234
Q

In JavaScript, when is a function’s scope determined; when it is called or when it is defined?

A

defined

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