JavaScript

Question 1

What is the purpose of a loop?

Answer 1

To execute a block of code as long as specified condition is true

Question 2

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

Answer 2

The purpose of condition expression in a loop is to be tested each time loop runs. As long as condition is true loop keeps running

Question 3

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

Answer 3

repetition of a process

Question 4

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

Answer 4

only first time before loop starts

Question 5

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

Answer 5

before each loop iteration

Question 6

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

Answer 6

At the end of each loop iteration

Question 7

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

Answer 7

The word “object” refers to the structured representation of an HTML or XML document.

Question 8

What is a DOM Tree?

Answer 8

A collection of objects in the computer memory that represent the HTML elements that define a web page.

Question 9

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

Answer 9

document.querySelectorAll()

Question 10

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

Answer 10

console.dir()

Question 11

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

Answer 11

document.querySelector() takes a CSS selector string as its argument. And returns the first element that matches specified CSS selector.

Question 12

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

Answer 12

It takes CSS string selectors as argument and returns static NodeList representing a list of documents that match argument

Question 13

What is the purpose of events and event handling?

Answer 13

It’s to interact with users in a specific way depends on user actions

Question 14

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

Answer 14

addEventListener

Question 15

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

Answer 15

function object

Question 16

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

Answer 16

by calling className property

Question 17

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

Answer 17

due to the event bubbling

Question 18

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

Answer 18

tagName

Question 19

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

Answer 19

As argument it takes string as CSS selector, it’s heading towards document root until it finds a node that matches provided selector string

Question 20

How can you remove an element from the DOM?

Answer 20

By using remove() method -> element.remove()

Question 21

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 21

add eventListener to the parent element and verify from which element event come from (condition)

Question 22

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

Answer 22

yes

Question 23

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

Answer 23

focus

Question 24

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

Answer 24

blur

Question 25

What does the event.preventDefault() method do?

Answer 25

preventing refresh the page

Question 26

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

Answer 26

It refreshes webpage

Question 27

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

Answer 27

The HTMLFormElement.elements returns an HTMLFormControlsCollection

Question 28

What is the textContent property of an element object for?

Answer 28

textContent property let us add text value to an element object or check text value of an element object

Question 29

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

Answer 29

className and setAttribute

Question 30

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

Answer 30

it's reusable, we can use different data, we can run it whenever we want

Question 31

What is the event.target?

Answer 31

target property of the Event interface is a reference to the object onto which the event was dispatched.

Question 32

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

Answer 32

takes string as an argument. Checks if the element would be selected by specified CSS selector. Returns true or false const birds = document.querySelectorAll('LI') for (const bird of birds) { if (bird.matches('.endangered')) { console.log('whee') } }

Question 33

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

Answer 33

getAttribute()

Question 34

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 34

We would have to make a code for individual tabs

Question 35

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 35

we would have to use conditional statement each time

Question 36

What are serialization and deserialization?

Answer 36

taking data and put it into order, deserialization is opposite

Question 37

What is JSON?

Answer 37

JSON (JavaScript Object Notation) format for storing and transporting data.

Question 38

Why are serialization and deserialization useful?

Answer 38

taking data and organize it into an order, deserialization is opposite

Question 39

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

Answer 39

JSON.stringify()

Question 40

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

Answer 40

JSON.parse

Question 41

How to you store data in localStorage?

Answer 41

using localstorage.setItem() method

Question 42

How to you retrieve data from localStorage?

Answer 42

using localstorage.getItem() method

Question 43

What data type can localStorage save in the browser?

Answer 43

strings

Question 44

When does the 'beforeunload' event fire on the window object?

Answer 44

before closing application.

Question 45

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

Answer 45

different syntax calculator.add() vs add function(x + x) { ...}

Question 46

What is the defining characteristic of Object-Oriented Programming?

Answer 46

methods are behavior , values are data. data and methods can be in shared space

Question 47

What are the four "principles" of Object-Oriented Programming?

Answer 47

abstraction, encapsulation ,inheritance, polymorphism

Question 48

What is "abstraction"?

Answer 48

taking complex functionality and make it accessible

Question 49

What does API stand for?

Answer 49

application programing interface

Question 50

What is the purpose of an API?

Answer 50

all tools letting programs interact between each other

Question 51

What is this in JavaScript?

Answer 51

the this keyword refers to an object. Which object, it depends on how this is being invoked (used or called)

Question 52

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

Answer 52

meaning that 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 53

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

Answer 53

call time

Question 54

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

Answer 54

You can't , it's just definition

Question 55

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

Answer 55

if there is no function call it's window. If it's . its always method of that object

Question 56

What kind of inheritance does the JavaScript programming language use?

Answer 56

prototype-based-inheritance(prototypal)

Question 57

What is a prototype in JavaScript?

Answer 57

It's reusing existing objects that serve as prototype

Question 58

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 58

their grabbing it from prototype object

Question 59

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

Answer 59

On it's own prototype.

Question 60

What does the new operator do?

Answer 60

let you create object for a function ,new create plain js object, add property to the new object, binds new object instance as this ,return this if function doesn't return any object.

Question 61

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

Answer 61

prototype property

Question 62

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 62

using setTImeOut()

Question 63

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

Answer 63

setInterval()

Question 64

What do setTimeout() and setInterval() return?

Answer 64

number id

Question 65

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

Answer 65

one line, request method, request url and HTTP version

Question 66

What is AJAX?

Answer 66

Programing concept, build in HTML XMLHTTPRequest object is used to execute Ajax on webpages, allowing websites to load content onto the screen without refreshing the page

Question 67

What does the AJAX acronym stand for?

Answer 67

asynchronous JavaScript and XML

Question 68

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

Answer 68

XMLHttpRequest();

Question 69

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

Answer 69

load event

Question 70

What is Event Bubbling

Answer 70

Event bubbling is the order in which event handlers are called when one element is nested inside a second element, and both elements have registered a listener for the same event (a click, for example).

Question 71

What is Event Propagation

Answer 71

This is the blanket term for both event bubbling and event capturing

Question 72

What is Event Capturing Phase?

Answer 72

?

Question 73

What is Event Delegation

Answer 73

It's event handling pattern. We put single handler on common ancestor and call an event on particular element (event.target)