JavaScript

Question 1

What is the purpose of variables?

Answer 1

To store data that we can go back to later. Permanence of data

Question 2

How do you declare a variable?

Answer 2

var (variable name) then assignment operator (=) with variable value

Question 3

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

Answer 3

var keyword then variable name with the assignment operator (=)

Question 4

What characters are allowed in variable names?

Answer 4

$, letters, numbers, underscore (variable can’t begin with number

Question 5

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

Answer 5

words with lower case and upper case are completely separate things to JavaScript

Question 6

What is the purpose of a string?

Answer 6

To store characters in a row that JavaScript won’t read as code

Question 7

What is the purpose of a number?

Answer 7

To store numeric values

Question 8

What is the purpose of a boolean?

Answer 8

Act as an “on or off” switch (indicating true or false)

Question 9

What does the = operator mean in JavaScript?

Answer 9

Assignment operator to give something value

Question 10

How do you update the value of a variable?

Answer 10

You just redeclare that variable as normal, except without the keyword “var”, “let”, or “const”

Question 11

What is the difference between null and undefined?

Answer 11

undefined is the way JavaScript creates or says something is empty or has no value (empty area which could have been left empty for random reasons)

null is something that we HAVE assign to make something empty or have no value (empty parking lot is on purpose so we can fill it with cars)

Question 12

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

Answer 12

So that we can identify what exactly we are using the console.log method on.

Question 13

Give five examples of JavaScript primitives.

Answer 13

String, boolean, null, undefined, and numbers

Question 14

What data type is returned by an arithmetic operation?

Answer 14

number data type

Question 15

What is string concatenation?

Answer 15

it’s using the plus sign operator to combine two or more strings together

Question 16

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

Answer 16

it’s used for string concatenation or adding numbers together

Question 17

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

Answer 17

a boolean

the strict equality operator (three equal signs) checks for same value and type

Question 18

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

Answer 18

it adds the value of the right operand and a variable, then it assigns the result of that expression to the variable.

so a += 3 is the same as “var a = (a’s old value) + 3”

Question 19

What are objects used for?

Answer 19

objects are used to store a collection of data

Question 20

What are object properties?

Answer 20

object properties are the keys

Question 21

Describe object literal notation.

Answer 21

keyword ‘var’ followed by a name then ‘=’ followed by curly brackets ‘{ }’

Question 22

How do you remove a property from an object?

Answer 22

keyword ‘delete’ followed by object.property

Question 23

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

Answer 23

bracket notation or dot notation

Question 24

What are arrays used for?

Answer 24

For representing lists of data

Question 25

Describe array literal notation.

Answer 25

keyword ‘var’ followed by the variable name then an equal sign with square brackets [ ].

The square brackets are the only part of the array literal notation.

Question 26

How are arrays different from “plain” objects?

Answer 26

Main thing arrays use numeric indexes (not created by you) while objects have alphanumeric indexes. All arrays come with property name (.length) and it is automatic. You also add stuff into the array differently.

Arrays are more like grocery lists (we care how much is on it) while objects are more like a dictionary.

Question 27

What number represents the first index of an array?

Answer 27

arrayName[0]

Always starts at index 0

Question 28

What is the length property of an array?

Answer 28

It stores the total number of items in an array

Question 29

How do you calculate the last index of an array?

Answer 29

arrayName.length - 1

The length property stores a “true count.” So an array with two item the length is 2, which means we need to subtract 1.

Question 30

What is a function in JavaScript?

Answer 30

A repeatable block of code

Question 31

Describe the parts of a function definition.

Answer 31

the var keyboard, function keyword, optional function name, infinite parameters within parenthesis, and then opening curly brace for code block

Question 32

Describe the parts of a function call.

Answer 32

function name and then the arguments within parenthesis, followed by semi-colon

Question 33

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

Answer 33

function definition creates the function and tells it what to do.

function call makes the function do the code.

Question 34

What is the difference between a parameter and an argument?

Answer 34

A parameter is what a function takes when it is defined. (placeholder values)

An argument is what the function takes when it is called. (real values)

Question 35

Why are function parameters useful?

Answer 35

They’re placeholders for the future input values. It makes it easier to identify what the function is doing.

Question 36

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

Answer 36

It specifies a return value for the function and it exits/ends the function.

Question 37

Why do we log things to the console?

Answer 37

To see how our code is working. It’s a debugging tool to constantly check the output of our code.

Question 38

What is a method?

Answer 38

A function which is a property of an object

Question 39

How is a method different from any other function?

Answer 39

A method is predefined? Methods are functions part of an object.

Question 40

How do you remove the last element from an array?

Answer 40

array.pop()

No value needed in parenthesis

Question 41

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

Answer 41

Math.floor()

It returns the largest integer less than or equal to a given number. So 5.95 is equal to 5, but -3.23 is equal to 3. Math.trunc() does something similar

Math.round is for nearest integer

Question 42

How do you generate a random number?

Answer 42

Math.random()

Only goes from 0 up to, but not including 1

Question 43

How do you delete an element from an array?

Answer 43

array.splice()

first parameter is starting point, second parameter is how many deletions, and third parameter is an optional and infinite number of items to add.

Question 44

How do you append an element to an array?

Answer 44

array.push(‘element’) adds to the end of an array because it’s asking “APPEND” which means add to the end.

while,
array.unshift(‘element’) adds to the front of an array

*infinite # of elements can be taken

Question 45

How do you break a string up into an array?

Answer 45

string.split() with the parameters being the indicator for what to split the string by. There’s also an optional limit parameter for setting the limit of substrings in the array.

Question 46

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

Answer 46

No, Strings are immutable so can’t modify them. To check we would use the console: assign any string to a variable, use the split method with a separator for each character, and then type the string variable again.

Question 47

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

Answer 47

A lot…40-50

Question 48

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

Answer 48

No, sometimes we are just concerned on what the method is doing rather than its return. For example, splice() returns an array of the deleted elements, but we are more concerned with the original array that splice was used on.

Question 49

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

Answer 49

A lot…40-50

Question 50

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

Answer 50

MDN

Question 51

Give 6 examples of comparison operators.

Answer 51

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

Question 52

What data type do comparison expressions evaluate to?

Answer 52

ALWAYS a boolean (true or false)

Question 53

What is the purpose of an if statement?

Answer 53

do determine if something is true or false, then execute some code based on that value

different behavior based on different data (allow us to make decisions)

Question 54

Is else required in order to use an if statement?

Answer 54

no it’s not

Question 55

Describe the syntax (structure) of an if statement.

Answer 55

if keyword, followed by parenthesis enclosing the test condition that compares two operands with a comparison operator then opening/closing curly brace.

Question 56

What are the three logical operators?

Answer 56

&& (and), || (or), and ! (returns opposite value)

Question 57

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

Answer 57

Logical && operator and logical || operator (often called ‘pipes’ or vertical bar)

Question 58

What is the purpose of a loop?

Answer 58

A way to do something more than once without typing it all out ourselves

Question 59

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

Answer 59

To set a stopping point for the loop, it’s the brakes

Question 60

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

Answer 60

A single time that the code block runs

Question 61

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

Answer 61

Before each iteration to decide whether we should stop or not

Question 62

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

Answer 62

Only at the start, before the first iteration. (it is the first thing that happens before anything else in the loop and it never happens again)

Question 63

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

Answer 63

Happens after the initialization and before each iteration of the loop

Question 64

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

Answer 64

After running the code block, but before the condition runs again

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

The keyword break

Question 66

What does the ++ increment operator do?

Answer 66

Increments the operand by 1, BUT it also reassigns the value.
We can use += to increment by more than 1.

i++ vs ++i

Ex: if counter = 1

counter++ + counter++ + ++counter + counter++
1 + 2 + 4 + 4 = 11
2 = 3 = 4 = 5

Answer is 11 for expression. Counter would equal 5.

Question 67

How do you iterate through the keys of an object?

Answer 67

With a “for in” loop

For var KEYS in OBJECTS; If you need to loop through an object, use for in loop.

Question 68

Why do we log things to the console?

Answer 68

We log things so that we can be sure that we are targeting/writing code for the right element or to evaluate values

Question 69

What is a “model”?

Answer 69

A copy of the tree of objects of the HTML page

Question 70

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

Answer 70

The entire html document

Question 71

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

Answer 71

Refers to the data type “object” in JavaScript

Question 72

What is a DOM Tree?

Answer 72

A DOM Tree is a parent element and all of it’s child nodes (a single element and ALL of its content)

DOM definition = A javascript object that is a model of the HTML document (it’s just a copy though)

Question 73

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

Answer 73

document. querySelector() and document.getByElementID()

* Should only use document.querySelector() for a single element

Question 74

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

Answer 74

document. getElementByClassName()
document. querySelectorAll()
* Should only use document.querySelectorAll() for multiple elements

Question 75

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

Answer 75

So that you can easily use the location of the element(s) more than once

*It’s common practice to use ‘$’ at the start of a variable name for a DOM method.
It also lets you reuse the same variable name without a $ for something else

Question 76

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

Answer 76

console. dir() - shows everything about the element, but console.log() gives a better visual representation
* Be sure to NOT include a ‘label’ because it doesn’t work with one

Question 77

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

Answer 77

To control the order in which things load on the webpage (loads from top to the bottom). We put the script tag at the bottom so it allows the HTML/CSS to load first before we access their elements with JavaScript.

Question 78

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

Answer 78

It takes any CSS selector. It returns ONLY the first matching element

• Be sure to have argument wrapped in quotes and as you would write it in CSS
  ex: (“.className”)

Question 79

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

Answer 79

It takes any CSS selector. It returns ALL matching elements into a nodelist

Question 80

Why do we log things to the console?

Answer 80

To check what we are working on and to debug scripts

Question 81

What is the purpose of events and event handling?

Answer 81

Events monitor user inputs which we can use with event handling to execute some code

Question 82

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

Answer 82

No

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

event.addEventListener()

Question 84

What is a callback function?

Answer 84

A callback function is a function passed into another function by its definition rather than being called.

Note: function definitions are saved as a type of data by JavaScript

Question 85

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

ex: function mouseClick(event);
$p.addEventListener(‘click’, mouseClick);

We are referring to the event parameter

Answer 85

An object with all the data of the event that just occurred

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

event.target is a property of the event object which points to the element WHERE the event occurred. Console.log or google it, more info on mdn.

Note: the “event” we are referring to is NOT the event we pass through

Question 87

What is the difference between these two snippets of code?

1. element.addEventListener(‘click’, handleClick)
2. element.addEventListener(‘click’, handleClick())

Answer 87

The first one is using a function definition and the second one is calling the function.

There is NEVER a return for an event handler function. So if we use the second one then the function will be replaced with the function return in this case, nothing or undefined.

Question 88

What is the className property of element objects?

Answer 88

It gets and sets the class attribute of the specified element

*Good to note that the className property is not the same as the attribute of the html element, it’s just a copy

Question 89

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

Answer 89

You have to query for the element then use the element.className property.

Ex: element.className = ‘apples’

Question 90

What is the textContent property of element objects?

Answer 90

The textContent property represents the text content of the specified node and all its descendants (child elements)

Question 91

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

Answer 91

You have to query for the element then use the textContent property

Ex: document.querySelector(‘div’).textContent = ‘new text content’

Question 92

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

Answer 92

No not always.

*Good to note that you should always include the event parameter so that we can easily identify an event handler function. This tells us we are never calling the function ourself and it tells us that it’s being done in response to something

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

It would be more complicated because we’d have to do more steps in order to reach the same output.

Question 94

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

Answer 94

It makes the information we stored easier to access in the future

Question 95

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

Answer 95

A focus event

Question 96

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

Answer 96

A blur event

Question 97

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

Answer 97

Input event

Question 98

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

Answer 98

Submit event

Question 99

What does the event.preventDefault() method do?

Answer 99

Prevents the default action of an event. In the case of the form exercise, it stopped the form from refreshing the page with the form values in the URL, which is its default action.

Question 100

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

Answer 100

The page automatically refreshes with the form values in the URL, which is its default action.

Question 101

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

Answer 101

The elements property of the form

Question 102

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

Answer 102

form.element.elementAttribute.value

The ‘value’ property

Question 103

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

Answer 103

You won’t know which part of your code is the problem. If you check the functionality of your code frequently then you can have an easier time in identifying the problem

*You should always do your code one step at a time and then test it

Question 104

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

Answer 104

You can check to see if the output of your code is what you actually expect it to produce.

Question 105

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

Answer 105

No, it creates a new element

Note: Always make dom tree that doesn’t change actual HTML and is in a function. That way you can always add it in if you want to

Question 106

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

Answer 106

You use append.child method which adds the new element as the last child.
You use insertBefore() to add an element where you want or at the front.

Syntax:

• element.appendChild();
• element.insertBefore(new item, target);

Question 107

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

Answer 107

You pass the attribute name then the attribute value

Question 108

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

Answer 108

You need to create a new element with documnent.createElement(), then you CAN set its attributes with element.setAttribute(), then you CAN set its text content with element.textContent = ‘ ‘; and then you need to append it to a parent element with element.appendChild().

*Note you need to querySelector() the parent element before appendChild()

Question 109

What is the textContent property of an element object for?

Answer 109

It’s used to set or access the text content of an element

Question 110

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

Answer 110

You can use element.setAtribute() or element.className = ‘ ‘;

Question 111

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

Answer 111

The main advantage is that it makes it super easy to test your code.
Ex: What’s the point of getting ALL the pokemon to show if we can’t even get the DOM tree for ONE pokemon

Another benefit is being able to name and reuse a chunk of code

Question 112

What is the event.target?

Answer 112

It’s the object where the event occurred??

Question 113

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

Answer 113

Because of a thing called event flow.

Event bubbling = event starts at most specific node (event.target) and flows out to the least specific node

Event capturing = event starts at least specific node and flows into the most specific one (event.target)

Question 114

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

Answer 114

event.target.tagName

short answer = .tagName property of an element

Question 115

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

Answer 115

It takes a CSS selector string as its argument and it returns itself or the target element’s closest ancestor.

*Note: querySelector() digs into something, while closest() digs out from something

Question 116

How can you remove an element from the DOM?

Answer 116

Using the element.remove() method.

Question 117

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 117

Wrap whatever elements you want into a parent element, then add the event listener to the parent element.

Question 118

What is the event.target?

Answer 118

The read-only target property of the Event interface is a reference to the object onto which the event was dispatched. It is different from Event.currentTarget when the event handler is called during the bubbling or capturing phase of the event.

Question 119

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

Answer 119

Turns off the display of an element so that it has no effect on layout (the document is rendered as though the element did not exist). All descendant elements also have their display turned off. To have an element take up the space that it would normally take, but without actually rendering anything, use the visibility property instead.

Question 120

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

Answer 120

It checks if the element is the actual selector we are at. The return is a boolean.

Question 121

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

Answer 121

element.getAttribute()

Question 122

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

Answer 122

All steps of the solution

Question 123

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 123

Individually make an event handler for each tab.

Note: The HTML event handler would make itself active and then make everything else off

Question 124

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 124

A new if statement for each tab and view to cover every case.

Question 125

JavaScript-and-JSON

What is JSON?

Answer 125

It’s text based data which has similar format to a JavaScript object. It makes it so developers can send an object over a network or store it.

Data interchange format which lets you convert data into a string, but it can go from string to objects

Stands for JavaScript Object Notation

Question 126

JavaScript-and-JSON

What are serialization and deserialization?

Answer 126

Serialization: The process of converting an object into a stream of bytes to store the object or transmit it to memory, a database, or a file.

Deserialization: The process of fetching a stream of bytes (string) from a network or storage place and converting it back into an object.

*Note: 8 bits in a byte. In reference to binary code (010101 thing)

Question 127

JavaScript-and-JSON

Why are serialization and deserialization useful?

Answer 127

Serialization is useful because it lets us transfer an object over a network and/or store it in persistent storage (hardrive).

Deserialization is useful for getting this stored object/ sent object and converting it back into an actual object

Question 128

JavaScript-and-JSON

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

Answer 128

We turn it into a JSON file by using JSON.stringify() method

Question 129

JavaScript-and-JSON

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

Answer 129

We turn it back into an object by JSON.parse() method.

Question 130

JavaScript-local-storage

How to you store data in localStorage?

Answer 130

localStorage.setItem(keyName, keyValue)

Question 131

JavaScript-local-storage

How to you retrieve data from localStorage?

Answer 131

localStorage.getItem(keyName) and it returns null (could be something in the future, but currently nothing) if there’s nothing there

Question 132

JavaScript-local-storage

What data type can localStorage save in the browser?

Answer 132

ONLY strings

*Useful if formatted as JSON

Question 133

JavaScript-local-storage

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

Answer 133

When the window, document, and its files/resources are ABOUT to be unloaded. So before the user refreshes the page, exits out of it, etc.

Question 134

Javascript-custom-methods

What is a method?

Answer 134

A function which is a property of an object.

Question 135

Javascript-custom-methods

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

Answer 135

A method definition has the function KEYWORD with parameters being ASSIGNED to a property name and it has a function CODE BLOCK, while a method call has the original OBJECT NAME and an ARGUMENT LIST.

Question 136

Javascript-custom-methods

Describe method definition syntax (structure).

Answer 136

Method definition looks a lot like property. It has property key name being assigned a function key word with parameters then function code block.

Question 137

Javascript-custom-methods

Describe method call syntax (structure).

Answer 137

object name DOT method name then arguments

Question 138

Javascript-custom-methods

How is a method different from any other function?

Answer 138

Not much different except it’s housed in an object

Question 139

Javascript-custom-methods

What is the defining characteristic of Object-Oriented Programming?

Answer 139

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

Question 140

Javascript-custom-methods

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

Answer 140

The four principles are: abstraction, encapsulation, inheritance, and polymorphism.

Question 141

Javascript-custom-methods

What is “abstraction”?

Answer 141

abstraction is working with (possibly) complex things in a simpler way. *Knowing what something does without knowing how it does it.

Question 142

Javascript-custom-methods

What does API stand for?

Answer 142

It stands for application programming interface.

Question 143

Javascript-custom-methods

What is the purpose of an API?

Answer 143

The purpose of an API (roughly means computers interacting/speaking with each other) is to give programmers a way to interact with a system in a simplified, consistent fashion: aka, an abstraction.

“Software abstraction”

Question 144

Javascript-this

What is this in JavaScript?

Answer 144

It’s an implicit parameter of all JavaScript functions.

*Purpose = variable which holds the value of the current object you’re working with

Question 145

Javascript-this

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

Answer 145

It means it doesn’t have to be defined

Question 146

Javascript-this

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

Answer 146

Call time of the function

Question 147

Javascript-this

What does ‘this’ refer to in the following code snippet?

var character = {
  firstName: 'Mario',
  greet: function () {
    var message = 'It\'s-a-me, ' + this.firstName + '!';
    console.log(message);
  }
};

Answer 147

‘this’ refers to nothing (meaning doesn’t exist) because the property greet doesn’t have a method call.

you need to invoke the function so, character.greet() to give ‘this’ and a value.

*this is an implicit PARAMETER, which means it has no value until the function is called.

Question 148

Javascript-this

var character = {
  firstName: 'Mario',
  greet: function () {
    var message = 'It\'s-a-me, ' + this.firstName + '!';
    console.log(message);
  }
};

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

character.greet();

Answer 148

The result is: “It’s a me, Mario!”

Because this.firstName refers to the firstName property of character

Question 149

Javascript-this

var character = {
  firstName: 'Mario',
  greet: function () {
    var message = 'It\'s-a-me, ' + this.firstName + '!';
    console.log(message);
  }
};

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

var hello = character.greet;
hello()

Answer 149

Result is: “It’s a me, undefined!”

it’s actually ‘window.hello()’, so this refers to window which doesn’t have a property ‘firstName’ so it is undefined .

Character.greet refers to the greet property of character object, BUT hello() has no object.

Question 150

Javascript-this

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

Answer 150

It can be recognized as the “object to the left of the dot” when the function is called (as a method)

current object??

Question 151

Javascript-this

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

Answer 151

Look to the left of the dot. If there is no value to the left of the dot then its default value is the global window object.

Question 152

Javascript-this

Main benefit of using ‘this’?

Answer 152

It allows us to use objects methods with other objects.

Ex: If we have an object ‘student’ explicitly state a parameter, ‘firstName’, then we can only use that firstName for the student object.

Question 153

Javascript-prototypes

What kind of inheritance does the JavaScript programming language use?

Answer 153

It uses prototype-based inheritance which means it reuses other objects for behaviors (methods) or data (properties)

Question 154

Javascript-prototypes

What is a prototype in JavaScript?

Answer 154

A prototype is an object that contains properties and (mostly) methods that can be used by other objects.

Question 155

Javascript-prototypes

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?

Answer 155

They all have a prototype object which stores a bunch of methods that can be used by strings, arrays, objects, and numbers.

Question 156

Javascript-prototypes

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

Answer 156

In the prototype object it’s attached to

Question 157

Javascript-constructors

What does the new operator do?

Answer 157

It:

1. creates a blank JavaScript object
2. adds the property to the new object (__proto__) that links to the constructor function’s prototype object
3. Binds the newly created object instance as the ‘this’ context (‘this’ refers to object created)
4. Returns ‘this’ if the function doesn’t return an object

Question 158

Javascript-constructors

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

Answer 158

Prototype property

Question 159

Javascript-constructors

What does the instanceof operator do?

Answer 159

It tests to see if the prototype property of a constructor appears anywhere in the prototype chain of an object. It returns a boolean.

Question 160

Javascript-timers

What is a “callback” function?

Answer 160

It’s a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of action/routine.

*Simple: a function being passed as a value for another function

Question 161

Javascript-timers

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

Using the global setTimeout() function, which executes a function/piece of code once the timer ends.

*Note: It returns an Interval ID which uniquely identifies the interval. Only a method if called on the window, but nobody does that :/

Question 162

Javascript-timers

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

Answer 162

Using the setInterval() function, which repeatedly calls a function or code snipped, with a fixed time delay between each call.

*Note: It returns an Interval ID which uniquely identifies the interval. Only a method if called on the window, but nobody does that :/

Question 163

Javascript-timers

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

Answer 163

0 ms, so executes immediately. Technically waits for next event cycle.

Question 164

Javascript-timers

What do setTimeout() and setInterval() return?

Answer 164

They both return a unique interval ID, which can be used with clearInterval() and/or clearTimeout()

Note: DO NOT USE ID’s for math aka not to be used as actual numbers

Question 165

http-messages

What is a client?

Answer 165

A client is hardware or software requesting service from a server.

Question 166

http-messages

What is a server?

Answer 166

A hardware or software that provides a resource/service to other computers

Question 167

http-messages

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

Answer 167

GET method

Question 168

http-messages

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

Answer 168

1. An HTTP method to describe the action to be performed
2. The request target, usually a URL
3. HTTP version

Question 169

http-messages

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

Answer 169

1. Protocol version
2. Status code, indicating success or failure of request
3. Status text, a brief description of the status code to help a human understand the HTTP message

Question 170

http-messages

What are HTTP headers?

Answer 170

They’re additional info which the server or client can pass for an HTTP response or request. Grouped as: 1. response/request headers, 2. representation headers, and 3. general headers.

Question 171

http-messages

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

Answer 171

MDN

Question 172

http-messages

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

Answer 172

No it’s not required for both http request and response. Divided into 3 categories: 1. single-resource bodies on a single line: content-type/content-length, 2. multiple-resource bodies: consisting of different bits of information on the http, 3. For responses: single-resource bodies: consisting of a single file of unknown length, encoded by chunks with transfer-encoding set to chunked

Question 173

javascript-ajax

What is AJAX?

Answer 173

It’s a programming practice of building complex, dynamic webpages using a technology known as XMLHttpRequest. - From MDN

It’s a web application that can update data without the needing to refresh the page.

*Initially stood for Asynchronous JavaScript And XML

Question 174

javascript-ajax

What does the AJAX acronym stand for?

Answer 174

*Initially stood for Asynchronous JavaScript And XML

Question 175

javascript-ajax

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

Answer 175

XMLHttpRequest

Question 176

javascript-ajax

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

Answer 176

A load event

Question 177

javascript-ajax

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

Answer 177

Prototype inheritance, OOP