JavaScript

Question 1

• What is the purpose of variables?

Answer 1

o Variables create permanence in your data

o It creates a box and stores information

Question 2

• How do you declare a variable?

Answer 2

o Use a keyword like let or var.

Question 3

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

Answer 3

o Use an assignment operator (SINGLE EQUAL SIGN “=”)

Question 4

• What characters are allowed in variable names?

Answer 4

o _ underscore and $. BUT variable names CANNOT start with a numeric value.

Question 5

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

Answer 5

o String and string are different.

o It is not good practice to use variable names that are the same but with different casing.

Question 6

• What is the purpose of a string?

Answer 6

o JavaScript strings are for storing and manipulating TEXT.
o These character are written INSIDE quotes.
o The string object is used to represent and manipulate a sequence of characters

Question 7

• What is the purpose of a number?

Answer 7

o To store numeric values FOR calculations – mathematical operations

Question 8

• What is the purpose of a boolean?

Answer 8

o To express a value of True or false
o Kind of like a light switch –
o Necessary for conditions and comparisons
o Helpful to determine whether or not to execute or not. (ON/OFF | it IS or IS NOT)
o Purpose of Booleans is to make DECISIONS (Yes or No)

Question 9

• What does the = operator mean in JavaScript?

Answer 9

o Assigner

Question 10

• How do you update the value of a variable?

Answer 10

o Use the assignment operator and WOULD NOT USE the keyword.
o VAR keyword is only necessary when creating the variable for the first time.
o CONFUSING.
o Does this variable already exist in my code?

Question 11

• What is the difference between null and undefined?

Answer 11

o Null is assigned
 Null is a value that can only exist because someone has assigned it to something.
 It is purposeful – since someone intentionally put it there
o Undefined
 Undefined is organic.
 If there is no return value, it will come back as undefined.
 Undefined is assigned by the browser – the ONLY value that JS can use to say “nothing”

Question 12

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

Answer 12

o For clarity so that when we return to the code, we can see what we were working on and not get confused.
o Labels makes it clear what we were working with.

Question 13

• Give five examples of JavaScript primitives.

Answer 13

o String, number, Boolean, null, undefined.

Question 14

• What data type is returned by an arithmetic operation?

Answer 14

o Numbers – not necessarily integers.

Question 15

• What is string concatenation?

Answer 15

o Adding together multiple strings.
o Concatenation will NEVER change the original string.
o Strings are immutable.
o They can never, EVER change.

Question 16

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

Answer 16

o Summing numerical data or string concatenation.

Question 17

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

Answer 17

o Boolean

Question 18

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

Answer 18

o Shorthand for reassigning a value of the original variable to the new value.
o =+ will make a lasting change to something while + will add but will not save the previous value.

Question 19

• What are objects used for?

Answer 19

o Objects group together a set of variables and functions to create a model of something you would recognize from the real world.

o In an object, variables and functions take on new names.

Question 20

• What are object properties?

Answer 20

o In an object, variables become known as properties.
o If a variable is part of an object, it is called a PROPERTY.
o Properties tell us about the object, such as the name of a hotel or the number of rooms it has.
o Each individual hotel might have a different name and a different number of rooms.

Question 21

• Describe object literal notation.

Answer 21

o THEY ARE A SET OF CURLY BRACES
o Properties separated by a colon.
o Commas to separate lines.

Question 22

• How do you remove a property from an object?

Answer 22

To delete a property, use the delete keyword followed by the object name and property name.
ex: delete hotel.name;

Question 23

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

Answer 23

o Use a dot or the brackets

o Bracket notation might be used when a property is inside an existing object.

Question 24

• What are arrays used for?

Answer 24

o Allows us to group data types (typically alike – but can be different) and gives us a way to put it into a list format and helps us deal with them one item at a time and see the scope of each item.

Question 25

• Describe array literal notation.

Answer 25

o Enclosed in square brackets [ ] – separated by commas.

Question 26

• How are arrays different from “plain” objects?

Answer 26

o Arrays do not have individually named pieces of data – BUT are ordered sequentially numerically indexed.
o Arrays have an order and tell us how many properties are inside. Objects do NOT.
o To add data to an array, you use a method named PUSH.
o To add data to a property of an object, use the assignment operator.
o Arrays show and tell us how many things we are working with.

Question 27

• What number represents the first index of an array?

Answer 27

o 0 ZERO

Question 28

• What is the length property of an array?

Answer 28

o Property in all arrays

o Returns a true count of how many items are in that array.

Question 29

• How do you calculate the last index of an array?

Answer 29

o Write out the length property of the length object.

o Whatever the value is of the array object and subtract 1.

Question 30

• What is a function in JavaScript?

Answer 30

o A block of code

o A function in JavaScript is similar to a procedure—a set of statements that performs a task or calculates a value

Question 31

• Describe the parts of a function definition.

Answer 31

o Function keyword, optional name, parameter list (with optional parameters), code block, return

Question 32

• Describe the parts of a function call.

Answer 32

o Write the name of the function, parenthesis, and any number of arguments.
o What if there are no parameters?!
 EMPTY PARENTHESIS.
 A function call at its most basic form is the name and empty parenthesis.
 Without parenthesis, NOTHING happens.

Question 33

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

Answer 33

o Function call has the function name and argument.

o Function definition has function keyword – otherwise, it is a function call.

Question 34

• What is the difference between a parameter and an argument?

Answer 34

o Parameter is a placeholder that just stays there.

o Argument, actual value that takes space in the placeholder.

Question 35

• Why are function parameters useful?

Answer 35

o Without parameters, you’d have to create a new function for each use.
o Parameters provide mutability.

Question 36

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

Answer 36

o Causes the function to produce a value
o Prevents any more code in the function’s code block from being run. AKA – IT STOPS THE FUNCTION ENTIRELY!
o Functions that are meant to do a job won’t have a return BUT Functions that are meant to have a value WILL HAVE a return.

Question 37

• Why do we log things to the console?

Answer 37

o A window we can communicate with the code –
a debugging tool

o Log stuff out and see what values are being used!

Question 38

• What is a method?

Answer 38

• A method is a function which is a property of an object.
There are two kind of methods: Instance Methods which are built-in tasks performed by an object instance, or
Static Methods which are tasks that are called directly on an object constructor.

Question 39

• How is a method different from any other function?

Answer 39

o A function is a block of code

o A method requires you to specify what object that function is attached to USING DOT NOTATION. (library.push(js))

Question 40

• How do you remove the last element from an array?

Answer 40

o pop() method.

Question 41

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

Answer 41

o Floor method of the Math object. –> math.floor

Question 42

• How do you generate a random number?

Answer 42

o Math.random

(range 0 to 1… not including 1 – so, .9999999999)

Question 43

• How do you delete an element from an array?

Answer 43

o Math.splice

Question 44

• How do you append an element to an array?

Answer 44

o Push method

Question 45

• How do you break a string up into an array?

Answer 45

o Split method – give it a set of character and it will look for those character and chop them out.

Question 46

• Do string methods change the original string?

How would you check if you weren’t sure?

Answer 46

o It does not. No string methods EVER change the original string – they are IMMUTABLE!
o If not sure, you can console.log the method of the string.
o Log out the string and see if it changes!

Question 47

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

Answer 47

o Many many.

Question 48

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

Answer 48

o a return value is used where the function is an intermediate step in a calculation of some kind. You want to get to a final result, which involves some values that need to be calculated by a function. After the function calculates the value, it can return the result so it can be stored in a variable; and you can use this variable in the next stage of the calculation.

Question 49

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

Answer 49

o Many many.

Question 50

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

Answer 50

o MDN

Question 51

• Give 6 examples of comparison operators.

Answer 51

o Simply equal to

o NEVER USE = =

Question 52

• What data type do comparison expressions evaluate to?

Answer 52

o Booleans

Question 53

• What is the purpose of an if statement?

Answer 53

o To determine whether to run a code block and check a condition

Question 54

• Is else required in order to use an if statement?

Answer 54

o Nope

Question 55

• Describe the syntax (structure) of an if statement.

Answer 55

o If keyword with the condition which is evaluated to true/false
o If keyword, condition, code block.

Question 56

• What are the three logical operators?

Answer 56

o And &&
o Or ||
o Not !

Question 57

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

Answer 57

o Use AND / OR && or ||

Question 58

• What is the purpose of a loop?

Answer 58

o Loops offer us the ability to repeat a single step / an action

Question 59

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

Answer 59

o To evaluate when to stop

o In the absence of a condition, loops will go on forever.

Question 60

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

Answer 60

o One time that the code block gets run.

Question 61

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

Answer 61

o At the beginning before each iteration

(BEFORE the code block runs)

Question 62

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

Answer 62

o The initialization step occurs one time only,
before the loop begins

o BEFORE ANYTHING – the very first thing.

Question 63

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

Answer 63

o First time, after the initialization
o Every subsequent time, before the code block of the next iteration
 And after the final expression or the initialization

Question 64

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

Answer 64

o Before the condition and AFTER the code block.

Question 65

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

Answer 65

o Break.

Question 66

• What does the ++ increment operator do?

Answer 66

o Adds AND saves one to the variable

Question 67

• How do you iterate through the keys of an object?

Answer 67

o With a for – in loop

Question 68

• Why do we log things to the console?

Answer 68

o To ensure what your code is doing what you want it to do.

Question 69

• What is a “model”?

Answer 69

o A representation of something.

Question 70

• Which “document” is being referred to in the phrase Document Object Model?

Answer 70

o The HTML document

Question 71

• What is the word “object” referring to in the phrase Document Object Model?

Answer 71

o Data type that can refer to
o DOM is a javascript object that is modeling the html document’s content.

o The Document Object Model (DOM) is the data representation of the objects that comprise the structure and content of a document on the web.

Question 72

• What is a DOM Tree?

Answer 72

o All of the information necessary to convey ONE element and all of its content.
o All of the necessary data to make an element.

Question 73

• Give two examples of document methods that retrieve a single element from the DOM.

Answer 73

o getElementByID and querySelector
o the only method you need to retrieve a single element is QUERYSELECTOR.
o The reason is, querySelector can find anything you are looking for.

Question 74

• Give one example of a document method that retrieves multiple elements from the DOM at once.

Answer 74

o querySelectorAll

Question 75

• Why might you want to assign the return value of a DOM query to a variable?

Answer 75

o So you don’t have to continue calling the result over and over again.
o Get it once and hold onto it.

Question 76

• What console method allows you to inspect the properties of a DOM element object?

Answer 76

o console.dir
o logged elements will look like the html code.
o If you need to look closer, use dir and it will show you the actual details that element is associated with.

Question 77

• Why would a tag need to be placed at the bottom of the HTML content instead of at the top?

Answer 77

o You want elements to exist BEFORE you look for them.
o LOAD ORDER (html runs from top to bottom).
o All of the body info must load in FULL before looking for those elements.

Question 78

• What does document.querySelector() take as its argument and what does it return?

Answer 78

o Takes a string containing a CSS selector and it only returns that which matches that selector.

Question 79

• What does document.querySelectorAll() take as its argument and what does it return?

Answer 79

o Takes the string and returns all of the matching elements.

Question 80

• Why do we log things to the console?

Answer 80

o To check the functionality and accuracy of our code

Question 81

• What is the purpose of events and event handling?

Answer 81

o Event handling – allows the developer to do something with the code – INTERACTIVITY.

Question 82

• Are all possible parameters required to use a JavaScript method or function?

Answer 82

o No – some are optional (LIKE BOOLEANS)

Question 83

• What method of element objects lets you set up a function to be called when a specific type of event occurs?

Answer 83

o addEventListener – allows us to create a functionality that will occur when users click on an event.

Question 84

• What is a callback function?

Answer 84

o A function passed as an argument to another function. And that other function can use that function if it needs to

Question 85

• What object is passed into an event listener callback when the event fires?

Answer 85

o Event object (Page 246-247 in Duckett)
o Javascript is aware that this is a problem so what it does, when an event occurs, in that exact micro second, it creates an object from scratch and in that object there is all the relevant data – that way inside the handler definition, you can dig into that object and get specific information about that occurrence.

Question 86

• What is the event.target? If you weren’t sure, how would you check? Where could you get more information about it?

Answer 86

o Where the event originated
 console.log – log it out and inspect
 MDN – read the documentation.

Question 87

• What is the difference between these two snippets of code?

element. addEventListener('click', handleClick)
element. addEventListener('click', handleClick())

Answer 87

o The first one will execute when the task is triggered (e.g when the item is clicked)
o The second one will return an error

Question 88

• What is the className property of element objects?

Answer 88

o The className property of the Element interface gets and sets the value of the class attribute of the specified element

Question 89

• How do you update the CSS class attribute of an element using JavaScript?

Answer 89

o className property

o You need the DOM element dot notation and className (camelCase) assigned to the new object.

Question 90

• What is the textContent property of element objects?

Answer 90

o The textContent property returns:
The text content of the element and all descendants, with spacing and CSS hidden text, but without tags.
o All the text hidden or not.

Question 91

• How do you update the text within an element using JavaScript?

Answer 91

o Query the element somehow and then…

o textContent property to access it by assignment

Question 92

• Is the event parameter of an event listener callback always useful?

Answer 92

o Not always – vast majority of the time, it is.

Question 93

• Would this assignment be simpler or more complicated if we didn’t use a variable to keep track of the number of clicks?

Answer 93

o Variable needs to exist outside of the function block

o Query select the element that increases the click count

Question 94

• Why is storing information about a program in variables better than only storing it in the DOM?

Answer 94

o You want the data you use to be present in JS.

o It’s better to use data within the same language you are in rather than depending on other languages.

Question 95

What do we actually do to get data from a form?

Answer 95

We set up our own code to take data out of the form and work with it.

This helps to validate and use it before sending it to wherever we are sending it.
It is control.

Question 96

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

Answer 96

o Focus

Question 97

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

Answer 97

o Blur

Question 98

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

Answer 98

o Input

o JavaScript INPUT vs. JavaScript CHANGE EVENT – THEY ARE DIFFERENT!

Question 99

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

Answer 99

o Submit

Question 100

• What does the event.preventDefault() method do?

Answer 100

o It prevents the default action
o Make it your FIRST line of code IN the function.
o The default action should NOT be taken as it normally would.
 Example: Checkboxes, that by default have a check – would not be marked.
o event.preventDefault() is ALWAYS present with a Submit button.
 Otherwise, it will reload.

Question 101

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

Answer 101

o It will simply RELOAD the page.

Question 102

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

Answer 102

o Every dom element has a property named ELEMENTS and that Elements property contains all of the form controls.

Question 103

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

Answer 103

o The Value Property in the Form Control gives you the value.

Question 104

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

Answer 104

o It can be broken – amongst a variety of other things.

Question 105

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

Answer 105

o You can see the small push forward and progress with the development of the page.
o Keep track of code and logs and errors in real time.

Question 106

• Does the document.createElement() method insert a new element into the page?

Answer 106

o Not right away… not ever.

o By calling the createElement element, it will create it, but it will not be visible to the user.

Question 107

• How do you add an element as a child to another element?

Answer 107

o appendChild method.

Question 108

• What do you pass as the arguments to the element.setAttribute() method?

Answer 108

o Html does not have data types so no need to preserve data types.

Question 109

• What steps do you need to take in order to insert a new element into the page?

Answer 109

o Create the element, give some content, insert to the page (appendChildmethod),
o If we do not have a variable already holding that element, use a querySelector (seek out and find the element)
o With newly made elements, we have immediate access because you created it… but for existing elements, you have to look for it.
o Query the element, actually make the element you want to put in the dom, configure it with any necessary information, and call it.

Question 110

• What is the textContent property of an element object for?

Answer 110

o appendText to node….

o Give it a new piece of content or observe a new piece.??

Question 111

• Name two ways to set the class attribute of a DOM element.

Answer 111

o	setAttribute with string class
o	assign a new value to the property.

Question 112

• What are two advantages of defining a function to do create something (like the work of creating a DOM tree)?

Answer 112

o You can reuse it.
o You can call that function again to make the same structure multiple times
o Utilize for multiple contexts.
o Use more than once, yes, but ALSO in multiple situations.

Question 113

• What is the event.target?

Answer 113

o Property on the event object that is a reference where the event was fired from

Question 114

• Why is it possible to listen for events on one element that actually happen its descendent elements?

Answer 114

o Event bubbling

Question 115

• What DOM element property tells you what type of element it is?

Answer 115

o Tag name

o Could be node name – but no.

Question 116

• What does the element.closest() method take as its argument and what does it return?

Answer 116

o Argument is the CSS selector
o Closest ancestor.
o Closest is LITERALLY the opposite of the querySelector – querySelector only looks inward whilst closest works outward.
 TWIST: every dom element has a querySelector-
 So in this exercise there is a $tasklist that is holding the element, UL

Question 117

• How can you remove an element from the DOM?

Answer 117

o Use remove method (remove()) on the object or the dom element you want to remove.

Question 118

• If you wanted to insert new clickable DOM elements into the page using JavaScript, how could you avoid adding an event listener to every new element individually?

Answer 118

o Add it to its parent.

Question 119

• What is the event.target?

Answer 119

o A property on the event object which stores an element of the dom object to where the event originated from.

Question 120

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

Answer 120

o Removes that from the document flow = it is no longer visible.

Question 121

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

Answer 121

o It takes the CSS selector as a string and returns a Boolean that represents matches the selector as an argument

Question 122

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

Answer 122

o Call the getAttribute

o Argument will be a string which is the name of the attribute we want to retrieve.

Question 123

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

Answer 123

o	Any time you want to store it to a variable and check what you’re using.
o	Call a method
o	Comparison expressions
o	Variables you assign values to.
o	EVERY TIME YOU DO ANYTHING.

Question 124

• 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?

Answer 124

o Add an eventListener for individual actions.

o Doing that would be code that is not scalable nor would it grow nicely.

Question 125

• 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?

Answer 125

o A long list of if statements (a HUGE CONDITIONAL Block – again, not scalable).

Question 126

• What is JSON?

Answer 126

o Javascript object notation – a format for rendering data that follows the __ of js objects

Question 127

• What are serialization and deserialization?

Answer 127

o Serialization uses data where all of the data is in one continuous string – pieces of data lined up right next to each other.
o Deserialization takes the data that is one continuous string and reverts it back to its more complex state to make things easy to access.
 Think about Cody’s illulstration on packing for a trip and unpacking when you get back… from multiple locations to your bag… then back to their respective locations.

Question 128

• Why are serialization and deserialization useful?

Answer 128

o When you store data, you want an easy way to store it.

Question 129

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

Answer 129

o Use the stringify method and pass the json

Question 130

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

Answer 130

o Use the parse method

Question 131

• How do you store data in localStorage?

Answer 131

o Setitem method of the local storage object

Question 132

• How do you retrieve data from localStorage?

Answer 132

o Getdata method of the local storage object

Question 133

• What data type can localStorage save in the browser?

Answer 133

o JUST STRINGS

Question 134

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

Answer 134

o Right before you close.
o When the window document and resources are about to close
o (close/refresh/close the browser/crashes)

Question 135

• What is a method?

Answer 135

o A method is a function which is a property of an object.

Question 136

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

Answer 136

o Method definition will have the function code block including keyword and code block
o Method call will ….

Question 137

• Describe method definition syntax (structure).

Answer 137

o Object literal and send it to a variable
o Property name WITH Colon
o Function definition with or without a name (use the name of the property)

Question 138

• Describe method call syntax (structure).

Answer 138

o object.methodName(arguments)

Question 139

• How is a method different from any other function?

Answer 139

o Method is associated with an OBJECT

Question 140

• What is the defining characteristic of Object-Oriented Programming?

Answer 140

…

Question 141

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

Answer 141

…

Question 142

• What is “abstraction”?

Answer 142

o Process of reducing complexity to the bits the user needs to know.

Question 143

• What does API stand for?

Answer 143

o Application Programming Interface

Question 144

• What is the purpose of an API?

Answer 144

o To hide the internal details of how a system is architected.
o Gives us a more simplistic way to interact with a more complex system.
o Light switch…
o DOM is an API – it is not part of the JavaScript language … it was built in the periphery – a complex system that has access to the complexities of the page. Very complicated but we can simply use it.

Question 145

• What is ‘this’ in JavaScript?

Answer 145

o ‘this’ is different from explicit parameters

o implicit parameter to see where the object was invoked

Question 146

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

Answer 146

o it is available in a function’s code block even though it was never included in the function’s parameter list or declared with var.

Question 147

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

Answer 147

o Call time

Question 148

• What does this refer to in the following code snippet?

Answer 148

var character = {
  firstName: 'Mario',
  greet: function () {
    var message = 'It\'s-a-me, ' + this.firstName + '!';
    console.log(message);
  }
};
o	NOTHING – it is NOT being called.
o	Implicit parameter – very important to understand.

Question 149

• Given the above character object, what is the result of the following code snippet? Why?

Answer 149

character.greet();

o It’s-a-me, Mario!

Question 150

• Given the above character object, what is the result of the following code snippet? Why?

Answer 150

var hello = character.greet;
hello();
o	It’s-a-me, undefined!

Question 151

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

Answer 151

o Within a definition, you can’t guarantee that it will have any specific value. It’s a place holder for a future value.

Question 152

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

Answer 152

o Whatever is to the left of the dot… i.e. window.hello();

o Look to the left of the dot when the function is called as a method.

Question 153

• What kind of inheritance does the JavaScript programming language use?

Answer 153

o Prototypal inheritance in JavaScript a fairly simple concept (especially compared to this). The ultimate goal is to move properties and methods that we’d like to reuse into a “prototype” object and then tell other objects to simply delegate (verb) to that “prototype” object when they aren’t able to perform the required tasks themselves.

Question 154

• What is a prototype in JavaScript?

Answer 154

o a JavaScript prototype is simply an object that contains properties and (predominantly) methods that can be used by other objects.
o The prototype is responsible for being the focal point of the behavior that needs to be in one spot for all other methods to use.

Question 155

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

Answer 155

o Because all of those have a prototype and have a shared behavior used/borrowed for later on.

Question 156

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

Answer 156

o In the prototype object
o If there are three or four layers of prototype, it will begin at the nearest parent to the next and to the next. (prototypal chain)

Question 157

• What does the new operator do? READ MDN

Answer 157

o It allows us to invoke a function as an constructor function.
o THIS MEANS: It makes an empty object and it will take the __proto__ property and assigns it to the prototype function
 Points the
o 3 –
o 4 – It returns the object if no other is specified.
 In a constructor function, there is no return value (< 0.000001%).
 By not having a return, you get the default, which is to return the object you’ve created.

Question 158

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

Answer 158

o Prototype property

o Every function EVER has the prototype property and it is an object.

Question 159

• What does the instanceof operator do?

Answer 159

o It checks

o OBJECT –> instanceof –> CLASS

Question 160

• What is a “callback” function?

Answer 160

…

Question 161

• 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?

Answer 161

o setTimeout()

Question 162

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

Answer 162

o setInterval

Question 163

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

Answer 163

o Default time delay of zero.

Question 164

• What do setTimeout() and setInterval() return?

Answer 164

o setTimeout returns…
o setInterval returns…
o They both share the same ID pool.

Question 165

• What is AJAX?

Answer 165

o Ajax is a technique for loading data into part of a page without having to refresh the entire page.
o (Data is often sent in a format called JavaScript Object Notation (or JSON)

Question 166

• What does the AJAX acronym stand for?

Answer 166

o Asynchronous JavaScript and XML

o However, Ajax is no used to refer to a group of technologies that offer asynchronous functionality in the browser.

Question 167

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

Answer 167

o XMLHttpRequest

Question 168

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

Answer 168

o Load

Question 169

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

Answer 169

o They share a prototype object.