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Web Development > JavaScript (Senior Side) > Flashcards

JavaScript (Senior Side) Flashcards

1
Q

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

A

a structure that consists of one or more declarations and statements. I.e. function code block, conditional code block, loop code block.

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2
Q

What does block scope mean?

A

Anything within the code block can only be accessed within the code block.

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3
Q

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

A

block

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4
Q

What is the difference between let and const?

A

The value of const can’t be changed through reassignment and it can’t be redeclared.

The value of let can be changed through reassignment and it can be redeclared.

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5
Q

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

A

Because if const is an arrray or an object, its properties or items can be updated or removed.

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6
Q

How should you decide on which type of declaration to use? (Const or let)

A

Consider whether or not the value of the variable will need to be changed in the future.

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7
Q

What is the syntax for writing a template literal?

A

backticks ( ` ` )

use $ { } to insert variables

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8
Q

What is “string interpolation”?

A

the ability to substitute part of the string for the values of variables or expressions.

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9
Q

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

A

It can only return one expression

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10
Q

What is destructuring, conceptually?

A

a syntax that allows us to get specific properties of an object and store them in a variable

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11
Q

What is the syntax for Object destructuring?

A

const { value } = variable

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12
Q

What is a CLI?

A

Command Line Interface

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13
Q

What is the syntax for Array destructuring?

A

const [array] = variable

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14
Q

How can you tell the difference between destructuring and creating Object/Array literals?

A

the operands are reversed

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15
Q

What is the syntax for defining an arrow function?

A

(param) => {

}

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16
Q

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

A

It captures the value of the enclosing context instead of creating its own this context.

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17
Q

What are the three virtues of a great programmer?

A

Laziness

Impatience

Hubris

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18
Q

What is Node.js?

A

Node.js is a program that allows JavaScript to be run outside of the web browser.

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19
Q

What can Node.js be used for?

A

1.back ends for Web applications

2.command-line programs

3.any kind of automation that developers wish to perform.

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20
Q

What is a REPL?

A

Read-Eval-Print-Loop. it is an interactive shell that processes Node. js expressions.

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21
Q

When was Node.js created?

A

May 27, 2009

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22
Q

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

A

a global that provides information about, and control over, the current Node.js process.

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23
Q

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

A

type out the process variable

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24
Q

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

A

array

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25
Q

What is a JavaScript module?

A

a single .js file.

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26
Q

What 4 values are passed into a Node.js module’s local scope?

A

.exports

.require

__filename

__dirname

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27
Q

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

A

console

process

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28
Q

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

A

to be able to reuse values from other other modules

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29
Q

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

A

with the require ( ) function

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30
Q

What 3 things does the JS Event Loop do?

A

1.) executes the code
2.) collects and processes events
3.) executes queued sub-tasks.

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31
Q

What is different between “blocking” and “non-blocking” with respect to how code is executed?

A

Blocking code is synchronous

Non-blocking is asynchronous

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32
Q

What is a directory?

A

something that holds files and folders

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33
Q

What is a relative file path?

A

A path that refers to a location that is relative to a current directory.

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34
Q

What is an absolute file path?

A

a path that contains the root element and the complete directory list required to locate the file.

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35
Q

What module does Node.js include for manipulating the file system?

A

the ‘fs’ module

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36
Q

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

A

fs.writefile( )

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37
Q

Are file operations using the fs module synchronous or asynchronous?

A

asynchronous

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38
Q

What is NPM?

A

Node Package Manager

open source software registry for developers

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39
Q

What is a package?

A

a file that can be downloaded and used in a program

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40
Q

How can you create a package.json with npm?

A

npm init -y command

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41
Q

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

A

A dependency is a third-party bit of software that was probably written by someone else and ideally solves a single problem for you.

it is installed with npm.install

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42
Q

What happens when you add a dependency to a package with npm?

A

it is added to the node modules directory

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43
Q

How do you add express to your package dependencies?

A

npm install express

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44
Q

What Express application method starts the server and binds it to a network PORT?

A

the listen method

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45
Q

What is a GUI?

A

Graphical User Interface

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46
Q

How do you mount a middleware with an Express application?

A

app.use ( )

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47
Q

Which objects does an Express application pass to your middleware to manage the request/response lifecycle of the server?

A

request object, response object, next object

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48
Q

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

A

application / json

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49
Q

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

A

they indicate the desired action to be performed for a given resource.

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50
Q

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

A

Returns middleware that only parses JSON and only looks at requests where the Content-Type header matches the type option.

you need it when working with server requests and responses

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51
Q

What is PostgreSQL and what are some alternative relational databases?

A

It is an open source, relational database management system. Other examples include MySQL, SQL server, and oracle

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52
Q

What are (3) advantages of learning a relational database?

A
  1. You can store and use data sets that are
    related to each other.
  2. Data corruption is unlikely
  3. Support good guarantees about data
    integrity
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53
Q

What is one way to see if PostgreSQL is running?

A

sudo service postgresql status

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54
Q

What is a database schema?

A

A collection of tables

55
Q

What is a table?

A

a list of rows each having the same set of attributes.

56
Q

What is a row?

A

contains a set of attributes

57
Q

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

A

1.) It’s a programming language that allows you to interact with relational databases
2.) it is declarative rather than imperative

58
Q

How do you retrieve specific columns from a database table?

A

with the “select” keyword followed by the “name” of column, followed by “from”

59
Q

How do you filter rows based on some specific criteria?

A

with the “where” clause

60
Q

What are the benefits of formatting your SQL?

A

its easier to read

61
Q

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

A

= < > !=

62
Q

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

A

the “limit” clause

63
Q

How do you retrieve all columns from a database table?

A

with an asterisk *

64
Q

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

A

with the “order by” clause

65
Q

How do you add a row to a SQL table?

A

with the “insert” and “into” keywords

66
Q

What is a tuple?

A

one row / a list of values

67
Q

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

A

add the headers / top row

add values below, and insert each new row of values into a new ( ) below the previous

68
Q

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

A

with the “returning” keyword

69
Q

How do you update rows in a database table?

A

with the update and set statements

70
Q

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

A

because if you don’t, you will end up updating every row in the table

71
Q

How do you delete rows from a database table?

A

delete statement

72
Q

How do you accidentally delete all rows from a table?

A

DONT SPECIFY “WHERE”

73
Q

What is a foreign key?

A

a field or column in one table that points to another table

74
Q

How do you join two SQL tables?

A

use the “join” keyword

75
Q

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

A

use an alias

76
Q

What are some examples of aggregate functions?

A

every ( ), count ( ) , avg ( )

77
Q

What is the purpose of a group by clause?

A

when you want to separate rows into groups and perform aggregate functions on those groups of rows

78
Q

What are the three states a Promise can be in?

A

pending: initial state, neither fulfilled nor rejected.
fulfilled: meaning that the operation was completed successfully.
rejected: meaning that the operation failed.

79
Q

How do you handle the fulfillment of a Promise?

A

with the .then method

80
Q

How do you handle the rejection of a Promise?

A

with the .catch method

81
Q

What is Array.prototype.filter useful for?

A

quickly getting desired array values that meet the specified criteria

82
Q

What is Array.prototype.map useful for?

A

calling a provided function on every element in an array, and then returning a new array with the results

83
Q

What is Array.prototype.reduce useful for?

A

combining all the contents of an array into a single value

84
Q

What is “syntactic sugar”?

A

syntax within a programming language that is designed to make things easier to read or to express.

85
Q

What is the typeof an ES6 class?

A

function

86
Q

Describe ES6 class syntax.

A

class Name {
constructor (name) {

}
function ( ) {
 
} }
87
Q

What is “refactoring”?

A

the process of restructuring existing computer code to better organize it while not changing its functionality.

88
Q

What is Webpack?

A

a tool that lets you bundle your JavaScript applications (supporting both ESM and CommonJS)

89
Q

How do you add a devDependency to a package?

A

with the “npm install –save-dev” command

90
Q

What is an NPM script?

A

a convenient way to bundle common shell commands for your project.

91
Q

How do you execute Webpack with npm run?

A

use the “npm run build” command

92
Q

Name 3 ways that ES Modules are different from CommonJS modules

A

1.) Slightly more complicated syntax
2.) Designed for asynchronous loading
3.) Main use: browser

93
Q

What 3 kind of modules can Webpack support?

A

1.es modules
2. commonJS
3. AMD

94
Q

What is React?

A

React is a JavaScript library / framework for creating user interfaces.

95
Q

What is a React element?

A

a DOM element created using React

96
Q

How do you mount a React element to the DOM?

A

create root method, pass in react element, and render the root object

97
Q

What is Babel?

A

a toolchain that is mainly used to convert ECMAScript 2015+ code into a backwards compatible version of JavaScript

98
Q

What is a Plug-in?

A

a software component that adds a specific feature to an existing computer program.

99
Q

What is a Webpack loader?

A

transformations that allow you to pre-process files as you import or “load” them.

100
Q

What dev dependency do you need to make Babel and Webpack work together?

A

the “babel loader”

101
Q

What is JSX?

A

a syntax extension to JavaScript using react

102
Q

Why must the React object be imported when authoring JSX in a module?

A

access to the React objects is needed

103
Q

What 2 dev dependencies can make Webpack and Babel work together to convert JSX into valid JavaScript?

A

1.) ‘babel loader”
2.) @babel/plugin-transform-react-jsx

104
Q

What is a React component?

A

they are like javascript functions, and accept arbitrary inputs (called “props”) and return React elements describing what should appear on the screen

105
Q

How do you define a function component in React?

A

function Name (props) {

}

106
Q

How do you mount a component to the DOM?

A
  1. query dom for div with id of “root” and save to a const named “container”
  2. call createRoot method of ReactDOM object and pass in container
  3. call render method of root object and pass in ( < createdElement />) from the render function
107
Q

What are props in React?

A

objects used to pass data to a component

108
Q

How do you pass props to a component?

A

with { props } syntax

109
Q

How do you write JavaScript expressions in JSX?

A

The same way you’d write them in JS

110
Q

How do you create “class” component in React?

A

with the className keyword

111
Q

How do you access props in a class component?

A

with the “this” keyword

112
Q

What is the purpose of state in React?

A

To give you more control over a component

113
Q

How to you pass an event handler to a React element?

A

you provide a listener as a property (“onClick, “onSubmit”) when the element is initially rendered.

114
Q

What are controlled components?

A

An input form element whose value is controlled by React via “state”

115
Q

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

A

value, event handler

116
Q

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

A

.map ( )

117
Q

What is the best value to use as a “key” prop when rendering lists?

A

use something that uniquely identifies a list item among its siblings.

118
Q

What does express.static() return?

A

serves static files from the specified “root” argument (data type is a function)

119
Q

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

A

The directory name of the current module.

120
Q

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

A

joins all specified path segments that are entered as arguments into one path

121
Q

What does fetch() return?

A

a promise that is fulfilled once the response is available.

122
Q

What is the default request method used by fetch()?

A

GET

123
Q

How do you specify the request method (GET, POST, etc.) when calling fetch?

A

put it as the second argument, inside of an object:

{ method: GET }

124
Q

When does React call a component’s componentDidMount method?

A

immediately after the component is rendered to the DOM

125
Q

Name three React.Component lifecycle methods.

A

render, constructor, componentDidMount

126
Q

How do you pass data to a child component?

A

use “props”

127
Q

What does the acronym LIFO mean?

A

Last In First Out

128
Q

What methods are available on a Stack data structure?

A

.peek ( )
.print( )
.push( )
.pop( )

129
Q

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

A

keep using .pop( ) until you reach the item you want

130
Q

What does the acronym FIFO mean?

A

first in first out

131
Q

What methods are available on a Queue data structure?

A

enqueue(value)
dequeue( )
print( )
peek( )

132
Q

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

A

use dequeue( ) until you reach the item you want

133
Q

How are linked lists different from an array?

A

they contain nodes

134
Q

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

A

the .next( ) method

Web Development (4 decks)

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