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Web Development > Javascript > Flashcards

Javascript Flashcards

1
Q

What is the purpose of variables?

A

To store data to be accessed later.

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2
Q

How do you declare a variable?

A

Var keyword variable Name; (var quantity;)

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3
Q

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

A

Var keyword var Name = var value; (var quantity = 3;)

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4
Q

What characters are allowed in variable names?

A

Letters, number, dollar sign, or underscore

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5
Q

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

A

Using the same variable name must have the same lowercase or uppercase letters.

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6
Q

What is the purpose of a string?

A

To store data made up of text

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7
Q

What is the purpose of a number?

A

To store numeric data / for tasks that involve counting or calculating

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8
Q

What is the purpose of a boolean?

A

To store true or false data / binary data.

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9
Q

What does the = operator mean in JavaScript?

A

Assignment

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10
Q

How do you update the value of a variable?

A

Variable name = new value;

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11
Q

What is the difference between null and undefined?

A

Null is intentionally left with no value and undefined is declared to variables that have not been assigned a value yet.

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12
Q

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

A

To add a description of the variable/value being logged.

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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

number

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15
Q

What is string concatenation?

A

Adding a string value with another value

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16
Q

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

A

Adds one value to another

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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 += “plus-equals” operator do?

A

It adds the value of the var on the right to the current value of the var on the left which then equals the var on the left.

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19
Q

What are objects used for?

A

To store multiple pieces of data in one variable / to organize data

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20
Q

What are object properties?

A

Individual variables stored in an object.

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21
Q

Describe object literal notation.

A

Var keyword variable name holding the object = { };

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22
Q

How do you remove a property from an object?

A

Delete operator . property name; OR delete property[‘property name’];

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23
Q

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

A

Dot notation and bracket notation

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24
Q

What are arrays used for?

A

To store a list of values. (mainly for similar data)

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25
Q

Describe array literal notation.

A

Var keyword variableName = [ ];

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26
Q

How are arrays different from “plain” objects?

A

The key for its’ value is a numeric index.

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27
Q

What number represents the first index of an array?

A

0

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28
Q

What is the length property of an array?

A

.length / holds the number of pieces of data in the array.

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29
Q

How do you calculate the last index of an array?

A

Array.length - 1;

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30
Q

What is a function in JavaScript?

A

Special type of object that can be called. Set of reusable code.

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31
Q

Describe the parts of a function definition.

A

Function keyword optionalFuncName ( parameter, ) {
Optional Return;
}

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32
Q

Describe the parts of a function call.

A

functionName()

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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

Call passes in argument/values .. definition has code block

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34
Q

What is the difference between a parameter and an argument?

A

Parameter is in definition(placeholder) and argument is in call(value).

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35
Q

Why are function parameters useful?

A

Gives more uses to the function since data can be passed in through the parameter.

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36
Q

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

A

Produce a value /

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37
Q

Why do we log things to the console?

A

To see if the code runs properly / check if any errors

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38
Q

What is a method?

A

A function stored within a property in an object.

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39
Q

How do you remove the last element from an array?

A

array.pop()

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40
Q

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

A

math.floor()

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41
Q

How do you generate a random number?

A

math.random()

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42
Q

How do you delete an element from an array?

A

array.splice()

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43
Q

How do you append an element to an array?

A

.push()

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44
Q

How do you append an element to an array?

A

.push() / .unshift()

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45
Q

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

A

No.

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46
Q

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

A

Not always.

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47
Q

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

A

36

48
Q

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

A

MDN

49
Q

Give 6 examples of comparison operators.

A

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

50
Q

What data type do comparison expressions evaluate to?

A

boolean.

51
Q

What is the purpose of an if statement?

A

to make a decision in the code.

52
Q

Is else required in order to use an if statement?

A

No.

53
Q

Describe the syntax (structure) of an if statement.

A

if (condition {
code to execute;
}

54
Q

What are the three logical operators?

A

Logical and (&&), Logical or(||), Logical not (!)

55
Q

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

A

using logical operator.

56
Q

What is the purpose of a loop?

A

To check if a condition is true.

57
Q

What does the ++ increment operator do?

A

Increments by 1.

58
Q

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

A

Focus

59
Q

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

A

Blur

60
Q

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

A

Input

61
Q

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

A

Submit

62
Q

What does the event.preventDefault() method do?

A

Prevents page from refreshing

63
Q

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

A

Refreshed the page

64
Q

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

A

Elements property.

65
Q

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

A

Value property.

66
Q

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

A

Harder to find where errors are happening.

67
Q

What is an advantage of having your console open when writing a JavaScript program?

A

To know right away if you have a bug.

68
Q

What is JSON?

A

String format meant to replicate javascript objects

69
Q

What are serialization and deserialization?

A

Serialization - taking data and converting it into a string of bytes. deserialization is taking bytes and turn it back into an object

70
Q

Why are serialization and deserialization useful?

A

Makes it possible to transfer data.

71
Q

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

A

stringify method of the JSON object.

72
Q

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

A

parse method of the JSON object.

73
Q

How to you store data in localStorage?

A

localStorage.setItem()

74
Q

How to you retrieve data from localStorage?

A

localStorage.getItem()

75
Q

What data type can localStorage save in the browser?

A

string

76
Q

What is a method?

A

A functions that is a property of an object.

77
Q

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

A

Method definition is code block being assigned to a property and call is object .methodName.

78
Q

Describe method definition syntax (structure).

A 
var keyword var name = {
method name: function keyword()
code block / return
}
79
Q

Describe method call syntax (structure).

A

object.methodName( );

80
Q

How is a method different from any other function?

A

Method is associated with objects.

81
Q

What is the defining characteristic of Object-Oriented Programming?

A

Objects contain data (as properties) as well as the behavior (as methods)

82
Q

What is “abstraction”?

A

Working with complex things in a simple way

83
Q

What does API stand for?

A

Application Programming Interface

84
Q

What is the purpose of an API?

A

connect two computers or softwares

85
Q

What is the purpose of an API?

A

Collection of tools for somebody else to use. Abstraction.

86
Q

What is this in JavaScript?

A

Keyword referring to an object - which you are doing work in / Implicit parameter of all JavaScript functions

87
Q

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

A

It is available to use in the function even though it was never included as a parameter or declared with var.

88
Q

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

A

Call time.

89
Q

How can you tell what the value of this will be for a particular function or method definition?

A

You can’t.

90
Q

How can you tell what the value of this is for a particular function or method call?

A

method - The object to the left of the dot. function - window.

91
Q

What kind of inheritance does the JavaScript programming language use?

A

Prototype based (prototypal)

92
Q

What is a prototype in JavaScript?

A

An original model of which something is patterned and added more unique features

93
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

It is a shared location

94
Q

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

A

Looks in the object prototype

95
Q

What does the new operator do?

A

Creates new object, adds new object (__proto__), binds created object as the “this” constructor function, returns “this”

96
Q

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

A

prototype

97
Q

What does the instanceof operator do?

A

Checks if thing on the left is the same as the proto type of the var on the right.

98
Q

What is a “callback” function?

A

a function passed into another function as an argument, thats called inside the outer function

99
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

Using the setTimeout( ) method

100
Q

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

A

setInterval() method

101
Q

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

A

0

102
Q

What do setTimeout() and setInterval() return?

A

Number that identifies the interval or timeout

103
Q

What is a client?

A

Something that is requesting information.

104
Q

What is a server?

A

The server provides/responds the information and is listening for requests.

105
Q

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

A

GET Method

106
Q

What three things are on the start-line of an HTTP request message?

A

The method, the target, and the HTTP version

107
Q

What three things are on the start-line of an HTTP response message?

A

Protocol version, status code, and status text

108
Q

What are HTTP headers?

A

Additional information for descriptions.

109
Q

Where would you go if you wanted to learn more about a specific HTTP Header?

A

MDN

110
Q

Is a body required for a valid HTTP request or response message?

A

NO

111
Q

What is AJAX?

A

programming practice of building complex, dynamic webpages using XMLHttpRequest

112
Q

What does the AJAX acronym stand for?

A

Asynchronous Javascript And XML

113
Q

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

A

XHR object

114
Q

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

A

Load Event

115
Q

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

A

They have a shared object in their prototypal chain.

Web Development (4 decks)

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