Javascript Flashcards
(115 cards)
1
Q
What is the purpose of variables?
A
To store data to be accessed later.
2
Q
How do you declare a variable?
A
Var keyword variable Name; (var quantity;)
3
Q
How do you initialize (assign a value to) a variable?
A
Var keyword var Name = var value; (var quantity = 3;)
4
Q
What characters are allowed in variable names?
A
Letters, number, dollar sign, or underscore
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.
6
Q
What is the purpose of a string?
A
To store data made up of text
7
Q
What is the purpose of a number?
A
To store numeric data / for tasks that involve counting or calculating
8
Q
What is the purpose of a boolean?
A
To store true or false data / binary data.
9
Q
What does the = operator mean in JavaScript?
A
Assignment
10
Q
How do you update the value of a variable?
A
Variable name = new value;
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.
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.
13
Q
Give five examples of JavaScript primitives.
A
String, number, boolean, undefined, null.
14
Q
What data type is returned by an arithmetic operation?
A
number
15
Q
What is string concatenation?
A
Adding a string value with another value
16
Q
What purpose(s) does the + plus operator serve in JavaScript?
A
Adds one value to another
17
Q
What data type is returned by comparing two values (, ===, etc)?
A
Boolean
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.
19
Q
What are objects used for?
A
To store multiple pieces of data in one variable / to organize data
20
Q
What are object properties?
A
Individual variables stored in an object.
21
Q
Describe object literal notation.
A
Var keyword variable name holding the object = { };
22
Q
How do you remove a property from an object?
A
Delete operator . property name; OR delete property[‘property name’];
23
Q
What are the two ways to get or update the value of a property?
A
Dot notation and bracket notation
24
Q
What are arrays used for?
A
To store a list of values. (mainly for similar data)
25
Describe array literal notation.
Var keyword variableName = [ ];
26
How are arrays different from "plain" objects?
The key for its’ value is a numeric index.
27
What number represents the first index of an array?
0
28
What is the length property of an array?
.length / holds the number of pieces of data in the array.
29
How do you calculate the last index of an array?
Array.length - 1;
30
What is a function in JavaScript?
Special type of object that can be called. Set of reusable code.
31
Describe the parts of a function definition.
Function keyword optionalFuncName ( parameter, ) {
Optional Return;
}
32
Describe the parts of a function call.
functionName()
33
When comparing them side-by-side, what are the differences between a function call and a function definition?
Call passes in argument/values .. definition has code block
34
What is the difference between a parameter and an argument?
Parameter is in definition(placeholder) and argument is in call(value).
35
Why are function parameters useful?
Gives more uses to the function since data can be passed in through the parameter.
36
What two effects does a return statement have on the behavior of a function?
Produce a value /
37
Why do we log things to the console?
To see if the code runs properly / check if any errors
38
What is a method?
A function stored within a property in an object.
39
How do you remove the last element from an array?
array.pop()
40
How do you round a number down to the nearest integer?
math.floor()
41
How do you generate a random number?
math.random()
42
How do you delete an element from an array?
array.splice()
43
How do you append an element to an array?
.push()
44
How do you append an element to an array?
.push() / .unshift()
45
Do string methods change the original string? How would you check if you weren't sure?
No.
46
Is the return value of a function or method useful in every situation?
Not always.
47
Roughly how many array methods are there according to the MDN Web docs?
36
48
What three-letter acronym should you always include in your Google search about a JavaScript method or CSS property?
MDN
49
Give 6 examples of comparison operators.
, <=, >=, ==, !=.
50
What data type do comparison expressions evaluate to?
boolean.
51
What is the purpose of an if statement?
to make a decision in the code.
52
Is else required in order to use an if statement?
No.
53
Describe the syntax (structure) of an if statement.
if (condition {
code to execute;
}
54
What are the three logical operators?
Logical and (&&), Logical or(||), Logical not (!)
55
How do you compare two different expressions in the same condition?
using logical operator.
56
What is the purpose of a loop?
To check if a condition is true.
57
What does the ++ increment operator do?
Increments by 1.
58
What event is fired when a user places their cursor in a form control?
Focus
59
What event is fired when a user's cursor leaves a form control?
Blur
60
What event is fired as a user changes the value of a form control?
Input
61
What event is fired when a user clicks the "submit" button within a ?
Submit
62
What does the event.preventDefault() method do?
Prevents page from refreshing
63
What does submitting a form without event.preventDefault() do?
Refreshed the page
64
What property of a form element object contains all of the form's controls.
Elements property.
65
What property of form a control object gets and sets its value?
Value property.
66
What is one risk of writing a lot of code without checking to see if it works so far?
Harder to find where errors are happening.
67
What is an advantage of having your console open when writing a JavaScript program?
To know right away if you have a bug.
68
What is JSON?
String format meant to replicate javascript objects
69
What are serialization and deserialization?
Serialization - taking data and converting it into a string of bytes. deserialization is taking bytes and turn it back into an object
70
Why are serialization and deserialization useful?
Makes it possible to transfer data.
71
How do you serialize a data structure into a JSON string using JavaScript?
stringify method of the JSON object.
72
How do you deserialize a JSON string into a data structure using JavaScript?
parse method of the JSON object.
73
How to you store data in localStorage?
localStorage.setItem()
74
How to you retrieve data from localStorage?
localStorage.getItem()
75
What data type can localStorage save in the browser?
string
76
What is a method?
A functions that is a property of an object.
77
How can you tell the difference between a method definition and a method call?
Method definition is code block being assigned to a property and call is object .methodName.
78
Describe method definition syntax (structure).
```
var keyword var name = {
method name: function keyword()
code block / return
}
```
79
Describe method call syntax (structure).
object.methodName( );
80
How is a method different from any other function?
Method is associated with objects.
81
What is the defining characteristic of Object-Oriented Programming?
Objects contain data (as properties) as well as the behavior (as methods)
82
What is "abstraction"?
Working with complex things in a simple way
83
What does API stand for?
Application Programming Interface
84
What is the purpose of an API?
connect two computers or softwares
85
What is the purpose of an API?
Collection of tools for somebody else to use. Abstraction.
86
What is this in JavaScript?
Keyword referring to an object - which you are doing work in / Implicit parameter of all JavaScript functions
87
What does it mean to say that this is an "implicit parameter"?
It is available to use in the function even though it was never included as a parameter or declared with var.
88
When is the value of this determined in a function; call time or definition time?
Call time.
89
How can you tell what the value of this will be for a particular function or method definition?
You can't.
90
How can you tell what the value of this is for a particular function or method call?
method - The object to the left of the dot. function - window.
91
What kind of inheritance does the JavaScript programming language use?
Prototype based (prototypal)
92
What is a prototype in JavaScript?
An original model of which something is patterned and added more unique features
93
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?
It is a shared location
94
If an object does not have it's own property or method by a given key, where does JavaScript look for it?
Looks in the object prototype
95
What does the new operator do?
Creates new object, adds new object (__proto__), binds created object as the "this" constructor function, returns "this"
96
What property of JavaScript functions can store shared behavior for instances created with new?
prototype
97
What does the instanceof operator do?
Checks if thing on the left is the same as the proto type of the var on the right.
98
What is a "callback" function?
a function passed into another function as an argument, thats called inside the outer function
99
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?
Using the setTimeout( ) method
100
How can you set up a function to be called repeatedly without using a loop?
setInterval() method
101
What is the default time delay if you omit the delay parameter from setTimeout() or setInterval()?
0
102
What do setTimeout() and setInterval() return?
Number that identifies the interval or timeout
103
What is a client?
Something that is requesting information.
104
What is a server?
The server provides/responds the information and is listening for requests.
105
Which HTTP method does a browser issue to a web server when you visit a URL?
GET Method
106
What three things are on the start-line of an HTTP request message?
The method, the target, and the HTTP version
107
What three things are on the start-line of an HTTP response message?
Protocol version, status code, and status text
108
What are HTTP headers?
Additional information for descriptions.
109
Where would you go if you wanted to learn more about a specific HTTP Header?
MDN
110
Is a body required for a valid HTTP request or response message?
NO
111
What is AJAX?
programming practice of building complex, dynamic webpages using XMLHttpRequest
112
What does the AJAX acronym stand for?
Asynchronous Javascript And XML
113
Which object is built into the browser for making HTTP requests in JavaScript?
XHR object
114
What event is fired by XMLHttpRequest objects when they are finished loading the data from the server?
Load Event
115
An XMLHttpRequest object has an addEventListener() method just like DOM elements. How is it possible that they both share this functionality?
They have a shared object in their prototypal chain.
