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LFZ C-0521 > JavaScript > Flashcards

JavaScript Flashcards

1
Q

What is the purpose of variables?

A

To store information to be accessed later on.

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2
Q

How do you declare a variable?

A

By using var , let, or const followed by the name of the variable.

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3
Q

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

A

By declaring a variable and then using the equal sign.

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4
Q

What characters are allowed in variable names?

A

letters, numbers, dollar signs

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5
Q

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

A

it means A and a are different

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6
Q

What is the purpose of a string?

A

The purpose of a string is to work with text and can contain HTML markup.

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7
Q

What is the purpose of a number?

A

To have a value that can be calculated. But also to determine screen sizes or an amount of time for an element to do something.

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8
Q

What is the purpose of a boolean?

A

To help determine when someone needs to happen or not. 1 or 0.

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9
Q

What does the = operator mean in JavaScript?

A

The equal sign operator means assign.

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10
Q

How do you update the value of a variable?

A

You would simply type the variable again without the var and assign a new value to it.

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11
Q

What is the difference between null and undefined?

A

Null is developer intended, while undefined is unintended.

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12
Q

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

A

There will be many logs when the codes get more in depth and things can get confusing. Simply, its for readability.

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13
Q

Give five examples of JavaScript primitives.

A

string, number, boolean, undefined, null

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14
Q

What data type is returned by an arithmetic operation?

A

A numerical value

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15
Q

What is string concatenation?

A

It’s when a string is added to another string or the value of a variable.

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16
Q

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

A

concatenation

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17
Q

What data type is returned by comparing two values (greater than, less than, ===, etc)?

A

Operands are being compared

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18
Q

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

A

It is the addition assignment. It adds the current value of something to the variable or number and the result of that expression is updated to the given variable.

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19
Q

What are objects used for?

A

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

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20
Q

What are object properties?

A

Object properties are essentially variables.

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21
Q

Describe object literal notation.

A

An object literal notation contains an opening curly brace that holds key value pairs, followed by a closing curly brace.

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22
Q

How do you remove a property from an object?

A

By using the delete operator followed by the object name and the property name.

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23
Q

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

A

By typing the object name followed by the member operator (.) followed by the assignment operator (=), followed by the new property value.

By typing the object name followed by the property name inside the square brackets followed by the equal sign and the new property value.

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24
Q

What are arrays used for?

A

Arrays are used to hold things like a shopping list or something that are closely related that can be referenced by index numbers.

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25
Q

Describe array literal notation.

A

An array notion has an opening square bracket followed by the a list of strings separated by commas and then closed off with a closing square bracket.

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26
Q

How are arrays different from “plain” objects?

A

Arrays can be accessed by index numbers while objects require dot notations.

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27
Q

What number represents the first index of an array?

A

0 zero

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28
Q

What is the length property of an array?

A

The length property would just be array.length.

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29
Q

How do you calculate the last index of an array?

A

The last index of an array is array.length - 1.

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30
Q

What is a function in JavaScript?

A

A tool in javascript to write scripts that can be reused as many times as needed.

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31
Q

Describe the parts of a function definition.

A

A function definition has a function keyword and name that can be anonymous or named, followed by parenthesis for the parameters, followed by a curly brace for the code block that has code inside to execute the given function when called.

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32
Q

Describe the parts of a function call.

A

Function call executes the function that is previously defined. It would be the name of the function along with the parenthesis.

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33
Q

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

A

A function definition has a code block that can be used over and over. While calling a function would execute the definition.

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34
Q

What is the difference between a parameter and an argument?

A

A parameter is used when defining a function, while an argument is used when calling a function.

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35
Q

Why are function parameters useful?

A

Parameters are placeholders for the arguments so the function would be dynamic (reusable), instead of it being hard coded.

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36
Q

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

A

Return allows the function to produce a value and also prevents more code from being run.

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37
Q

Why do we log things to the console?

A

To check what the line of code is doing so we can see if it’s correct.

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38
Q

What is a method?

A

Method is a function which is a property of an object. Methods are built-in for javascript and usually have a purposeful return value.

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39
Q

How is a method different from any other function?

A

Methods are already built-in to the language. Other functions, we would need to define it.

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40
Q

How do you remove the last element from an array?

A

Array.pop()

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41
Q

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

A

Math.floor()

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42
Q

How do you generate a random number?

A

Math.random()

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43
Q

How do you delete an element from an array?

A

Array.splice()

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44
Q

How do you append an element to an array?

A

Array.push(), Array.unshift(),

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45
Q

How do you break a string up into an array?

A

String.split()

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46
Q

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

A

You can log out the new variable if the string method was assigned.

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47
Q

Roughly how many string methods are there according to the MDN Web docs?

A

a lot

48
Q

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

A

Not always useful, but there was a use when someone created it.

49
Q

Roughly how many array methods are there according to the MDN Web docs?

A

a lot

50
Q

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

A

mdn

51
Q

Give 6 examples of comparison operators.

A

==, ===, !=, !==, >, =, <=

52
Q

What data type do comparison expressions evaluate to?

A

Boolean values.

53
Q

What is the purpose of an if statement?

A

If statements allow a statement to execute if the condition being compared is true.

54
Q

Is else required in order to use an if statement?

A

no.

55
Q

Describe the syntax (structure) of an if statement.

A

Keyword if followed by parenthesis. Inside is the condition thats being compared. Followed by a return value of some sort or action.

56
Q

What are the three logical operators?

A

logical and, logical or, logical not

57
Q

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

A

Using the logical operators.

58
Q

What is the purpose of a loop?

A

Loops are used to execute something over and over until the condition is met.

59
Q

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

A

The condition expression is our on and off setting for the loop.

60
Q

What does “iteration” mean in the context of loops?

A

It refers to each time the loop is run and then repeated.

61
Q

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

A

It gets evaluated in the beginning after the while keyword.

62
Q

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

A

It gets evaluated in the beginning of a for loop.

63
Q

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

A

After the initialization expression and after the start of each iteration.

64
Q

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

A

After the condition express if it was met and the code block within the loop is executed.

65
Q

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

A

break

66
Q

What does the ++ increment operator do?

A

The ++ adds one to the current value.

67
Q

How do you iterate through the keys of an object?

A

By using a for in loop.

68
Q

What is the event.target?

A

Refers to the object of the event that is occurring.

69
Q

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

A

It allows us to hide things from the html.

70
Q

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

A

it takes a CSS selector as a string

71
Q

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

A

element.getAttribute()

72
Q

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

A

From the very beginning.

73
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

.

74
Q

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?

A

.

75
Q

What is JSON?

A

JavaScript Object Notation

76
Q

What are serialization and deserialization?

A

Serialization is the process of turning an object in memory to a stream of bytes to be stored.
Deserialization is the process of turning a steam of bytes back into an object.

77
Q

Why are serialization and deserialization useful?

A

Allows computers to send data to one another in an efficient way.

78
Q

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

A

JSON.stringify()

79
Q

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

A

JSON.parse()

80
Q

How to you store data in localStorage?

A

localStorage.setItem()

81
Q

How to you retrieve data from localStorage?

A

localStorage.getItem()

82
Q

What data type can localStorage save in the browser?

A

strings

83
Q

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

A

The beforeunload event occurs when the browser is attempting to close/unloaded.

84
Q

What is a method?

A

A function which is a property of an object.

85
Q

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

A

A method definition has the keyword function and the code block following it. A method call only has the argument inside of the method.

86
Q

Describe method definition syntax (structure).

A

A method definition would have the property name followed by the function keyword and its parameters. And then a code block that has the necessary code.

87
Q

Describe method call syntax (structure).

A

A method call would have the object followed by a period and the property after. And then parenthesis to hold the given arguments for that method call.

88
Q

How is a method different from any other function?

A

A method is a property thats defined within that object, while a normal function is a method of the global scope (window).

89
Q

What is the defining characteristic of Object-Oriented Programming?

A

Objects can contain both data (as properties) and behavior (as methods).

90
Q

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

A

Abstraction, Encapsulation, Inheritance, Polymorphism

91
Q

What is “abstraction”?

A

Abstraction is the process of generalization for something that is much more complicated so it is easier to work with.

92
Q

What does API stand for?

A

Application Programming Interface

93
Q

What is the purpose of an API?

A

To allow a programmer a way to interact with a system in a simplified way.

94
Q

What is this in JavaScript?

A

This is an implicit parameter of all js functions.

95
Q

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

A

Means it is available in the code block even if it was never included in the parameter list.

96
Q

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

A

call time

97
Q

What kind of inheritance does the JavaScript programming language use?

A

prototype-based or prototypal

98
Q

What is a prototype in JavaScript?

A

An object that contains properties and methods that can be used by other objects.

99
Q

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

A

.

100
Q

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

A

.

101
Q

What does the new operator do?

A

.

102
Q

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

A

.

103
Q

What does the instanceof operator do?

A

The operator tests to see if the prototype property of a constructor appears anywhere in the prototype chain. A boolean value is returned.

104
Q

What is a “callback” function?

A

A callback function is a function passed into another function as an argument.

105
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

By using the method setTimeout.

106
Q

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

A

By using the setInterval method.

107
Q

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

A

The default time delay is 0, which executes immediately.

108
Q

What do setTimeout() and setInterval() return?

A

They both return a timeoutID that can be used to cancel the timeout.

109
Q

What is AJAX?

A

A programming practice of building complex, dynamic, webpages using XMLHttpRequest.

110
Q

What does the AJAX acronym stand for?

A

Asynchronous JavaScript and XML

111
Q

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

A

XMLHttpRequest

112
Q

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

A

load

113
Q

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

A

They both of the same eventTarget prototype.

114
Q

What is Array.prototype.filter useful for?

A

The array.filter method will help create a new array with all the elements that pass the test in the provided function.

115
Q

What is Array.prototype.map useful for?

A

Array.map is useful for converting lists of data into another format. Examples are times for time zone to a different time zone and currency values.

116
Q

What is Array.prototype.reduce useful for?

A

Array.reduce is useful for condensing data into smaller data to interpret easier. Outputs a single value.

LFZ C-0521 (13 decks)

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