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JavaScript Flashcards

1
Q

What is the purpose of variables?

A

to store data

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2
Q

How do you declare a variable?

A

variable keyword, variable name, assignment operator, and value
ex: var name = ‘Ashley’;

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3
Q

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

A

use the assignment operator (=)
variable keyword variable name = value
var greeting = ‘hello’;

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4
Q

What characters are allowed in variable names?

A

letters, numbers, $ or underscore
** however, variables cannot start with a number

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5
Q

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

A

Capitalization is taken into consideration when naming or calling variables
*means that two variables with the same name but different capitalization would be considered two variables
ex: var potato; vs var Potato;

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6
Q

What is the purpose of a string?

A

store/manipulate text that js won’t interpret as code

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7
Q

What is the purpose of a number?

A

represent and manipulate quantities/mathematical operations

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8
Q

What is the purpose of a boolean?

A

represents true/false, for decision making

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9
Q

What does the = operator mean in JavaScript?

A

a value is being assigned to a variable

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10
Q

How do you update the value of a variable?

A

use the variable name with assignment operator (=) and the new value

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11
Q

What is the difference between null and undefined?

A

Null indicates an intentional absence of a value, like a placeholder
*when you see null, that tells you that someone wanted it to be empty on purpose
undefined means there hasn’t been anything assigned to the variable
*JS way of communicating that there’s nothing there.

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12
Q

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

A

it provides you with more clarity and can help with debugging

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13
Q

Give 5 examples of JavaScript primitives

A

string, number, boolean, null, undefined

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14
Q

What data type is returned by an arithmetic operation?

A

Numbers

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15
Q

What is string concatenation?

A

joins two or more strings together

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16
Q

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

A

adds values together
*arithmetically if numbers
*concatenation if strings

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17
Q

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

A

boolean

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18
Q

what does the += operator do?

A

takes the value to the right of the operator and adds/concatenates it to the variable on the left and assigns the result of that expression to the variable

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19
Q

What are objects used for?

A

to group together variables and functions to create a model of something
Gives you ability to store multiple pieces of data under 1 name

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20
Q

What are object properties?

A

variables and their values

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21
Q

describe object literal notation

A

variable keyword name of object assignment operator
curly brace followed by properties and methods and their values
end curly brace
ex: var person {
name: ‘ashley’,
age: 29,
ethnicity: ‘vietnamese’
};

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22
Q

How do you remove a property from an object?

A

delete operator followed by objectname.propertyname;
or
delete operator followed by objectname[‘property.name’];

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23
Q

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

A

dot notation
ex: objectname.propertyname;
bracket notation
ex: objectname.[‘propertyname];

if you want to update the value, follow it with an assignment operator and the new value

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24
Q

What are arrays used for?

A

To store a list of values that are related to each other

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25
Describe array literal notation
pair of brackets, inside the brackets are values separated by commas
26
How are arrays different from "plain" objects?
objects store properties and their values while arrays have indexes and values to add to an object, use dot or bracket notation to add to an array, use the push method arrays also have length property while objects do not
27
What number represents the first index of an array?
0
28
What is the length property of an array?
it tells you the numbers of items in the array.
29
How do you calculate the last index of the array?
array.length - 1
30
What is a function in JavaScript?
A block of code designed to do a specific task
31
Describe the parts of a function definition
1. Function keyword 2. Optional name 3. Parameters ( 0 or more separated by commas) 4. Code block 5. Optional return statement
32
Describe the parts of a function's call.
1. Name of function 2. Any arguments being passed in between parentheses
33
When comparing them side-by-side, what are the differences between a function call and a function definition?
Function definitions are longer and can have parameters and a keyword Function calls are much simpler and can pass arguments
34
What is the difference between a parameter and an argument?
Parameters are like placeholders in the function definition, arguments are what's being passed when you call a function
35
Why are function parameters useful?
They act as placeholders that allow us to pass arguments when you call the function
36
What two effects does a return statement have on the behavior of a function?
exits the code block/prevents any more code in the block from being run allows the function to produce a value that you can utilize
37
Why do we log things to our console?
to observe and communicate with our code to check our work
38
What is a method?
a function that is associated/a property of an object
39
How is a method different from any other function?
you need to state the object you're calling it off on. ex: object.method() vs functionName()
40
How do you remove the last element of an array?
pop() method
41
How do you round a number down to the nearest integer?
floor() method
42
How do you generate a random number?
random() method --> gives you a value between 0 and 1 which you multiply by the string length
43
How do you delete an element from an array?
splice() method parameters are (start, deletecount, item1, itemN)
44
how do you append an element to an array?
push() method --> adds to the end of an array.
45
How do you preppend(add at the beginning) an element from an array?
unshift() method
46
how do you break a string up into an array?
split(separator, limit) method --> takes pattern, divides string into ordered list of substrings, puts strings into array, returns array
47
Do string methods change the original string? How would you check if you weren't sure?
No bc strings are immutable in JS Console.log the var the string is assigned to
48
How many string methods and array methods are there according to MDN?
Lots
49
Is the return value of a function or method useful in every situation?
Yes... potentially but the return value is not always necessary so no
50
What 3 letter acronym should you always include in your google search about a JS method or CSS property?
MDN
51
What's the purpose of a loop?
Checks a condition so a code block can run
52
What is the purpose of a condition expression in a loop?
to see if the expression evaluated is true/false so it knows to continue or terminate the loop
53
What does iteration mean in the context of loops?
It means to go a round, same steps being repeated multiple times
54
When does the condition expression of a while loop get evaluated?
at the beginning before executing the statement
55
When does the initialization expression of a for loop get evaluated?
first and only once
56
When does the condition expression of a for loop get evaluated?
right before each loop iteration/before the final expression
57
When does the final expression of a for loop get evaluated?
after the condition is found as true
58
Besides a return statement, which exits the entire function block, which keyword exits a loop before its condition expression evaluates to false?
break
59
What does the ++ increment operator do?
adds 1 to the operand and returns the value
60
How do you iterate through the keys of an object?
for... in loop
61
What is a "model"?
a blueprint/framework/display/reference
62
Which "document" is being referred to in the phrase Document Object Model?
HTML
63
What is the word "object" referring to in the phrase Document Object Model?
javascript elements
64
What is a DOM tree?
a model of the HTML document and all of it's parts recreated as javascript objects
65
Give two examples of document methods that retrieve a single element from the dom
getElementByID('id') querySelector('css selector')
66
Give one example of a document method that retrieves multiple elements from the DOM at once
querySelectorAll('css selector')
67
Why might you want to assign the return value of a DOM query to a variable?
It stores the location of an element in a variable – saves the browser time
68
What console method allows you to inspect the properties of a DOM element object?
console.dir() --> dir stands for directory
69
Why would a script tag need to be placed at the bottom of the HTML content instead of at the top?
html browsers load top to bottom this allows the html content to be loaded prior to the script being downloaded and executed
70
What does document.querySelector() take as its argument and what does it return?
the name of a selector surrounded by strings/quotes It returns the first element that matches the specified selector
71
What does document.querySelector() take as its argument and what does it return?
the name of the css selector returns all elements that match the specified selector called a node list
72
What is the purpose of events and event handling?
To create a dynamic webpage that users can interact with or respond to something that happens
73
Are all possible parameters required to use a JavaScript method or function?
no
74
What method of element objects lets you set up a function to be called when a specific type of event occurs?
addEventListener('event', functionName)
75
What is a callback function?
function passed into another function as an argument that will be called at some point
76
What object is passed into an event listener callback when the event fires?
The event object
77
What is the event.target?
the place where the event occurred - first element most immediate to where the event occurred
78
What is the difference between these two snippets of code? element.addEventListener('click', handleClick) element.addEventListener('click', handleClick())
The () indicates that the function is being called immediately rather than when the event fires
79
What is the className property of element objects?
It pulls OR sets the value of the class attribute of a specified HTML element
80
How do you update the CSS class attribute of an element using JS?
element.className= "name of class"
81
What is the textContent property of element objects?
It returns the text content of the element
82
How do you update the text within an element using JavaScript?
element.textcontent = text
83
Is the event parameter of an event listener callback always useful?
no
84
Why is storing info about a program in variables better than only storing it in the DOM?
It's about accessibility, it will be faster to access the variable than the DOM
85
What event is fired when a user places their cursor in a form control?
focus event
86
What event is fired when a user's cursor leaves a form control?
Blur event
87
What event is fired as a user changes the value of a form control?
Input event
88
What event is fired when a user clicks the "submit" button within a form?
submit event
89
What does the event.preventDefault() method do?
cancels the default action that belongs to the event (if its cancelable)
90
What does submitting a form without event.preventDefault() do?
it reloads/refreshes the page
91
What property of a form element object contains all of the form controls?
element property
92
What property of a form control object gets and sets its value?
value property
93
Does the document.createElement() method insert a new element into the page?
No, it only creates it but doesn't add it to the page
94
How do you add an element as a child to another element?
element.appendChild()
95
What do you pass as the arguments to the element.setAttribute() method?
name and value
96
What steps do you need to take in order to insert a new element into the page?
create the element, create the text node, and append it
97
Name two ways to set the class attribute of a DOM element
element.setAttribute() element.className
98
What are two advantages of defining a function to create something (like the work of creating a DOM tree?
allows you to use it over and over allows you to use it in different locations/context
99
Give two examples of media features that you can query in a @media rule
width, height, orientation
100
Which HTML meta tag is used in mobile-responsive web pages?
viewport meta tag
101
What is the event.target?
The target of the event // basically the element that was interacted with
102
Why is it possible to listen for events on one element that actually happens with its descendent elements?
Because of event bubbling
103
What DOM element property tells you what type of element it is?
element.target.tagName
104
What does the element.closest() method take as its argument and what does it return?
it takes a selector as the argument and returns the closest ancestor element or itself that matches the selectors
105
How can you remove an element from the DOM?
element.remove() <--- element is the one you want to remove
106
If you wanted to insert new clickable DOM elements into the page using JS, how could you avoid adding an event listener to every new element individually?
DOM event delegation
107
What is JSON?
text based format that represents structured data * in the form of a string *
108
What are serialization and deserialization?
Serialization takes an object in memory into a stream of bytes so you can do stuff with it or send it elsewhere Deserialization is the opposite: turning the stream of bytes into an object in memory
109
Why are serialization and deserialization useful?
It allows you to use data and recreate objects in different locations/platforms
110
How do you serialize a data structure into a JSON string using JavaScript?
JSON.stringify()
111
How do you deserialize a JSON string into a data structure using JavaScript?
JSON.parse()
112
How do you store data in localStorage?
localStorage.setItem(keyName, keyValue) keyName is in strings
113
How do you retrieve data from localStorage?
localStorage.getItem(keyName) keyName is in strings
114
What data type can localStorage save in the browser?
string data types
115
When does the 'beforeunload ' event fire on the window object?
Before the page unloads which can be refreshing the page or closing the tab anything that would cause the application to reload of close

LFZ Quiz Questions (9 decks)

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