Week 5

Question 1

What is a method?

Answer 1

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

Question 2

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

Answer 2

Method definition is the function inside an object which has a name followed by a colon, while method call is when you call its method with arguments or without arguments

Question 3

Describe method definition syntax (structure).

Answer 3

First you declare the object by creating a variable and equaling it to curly braces. Within the curly braces you have properties which can be given any name and then a colon. Following the colon you have a function. If you want to add more properties you have to add a comma at the end of the closing curly brace. If not, close the object with a closing curly brace followed by a semicolon.

Question 4

Describe method call syntax (structure).

Answer 4

You call the object name followed by a period, then the name of the property followed by parentheses with arguments if it has any.

Question 5

How is a method different from any other function?

Answer 5

A method is associated with a object and functions are not.

Question 6

What is the defining characteristic of Object-Oriented Programming?

Answer 6

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

Question 7

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

Answer 7

Abstraction, Encapsulation, Inheritance, Polymorphism

Question 8

What is “abstraction”?

Answer 8

Being able to work with (possibly) complex things in simple ways.

Question 9

What does API stand for?

Answer 9

Application Programming Interface

Question 10

What is the purpose of an API?

Answer 10

The purpose of API is to communicate between apps with each other as intermediary, where both apps might have been built with different tools and technologies.

Question 11

What is this in JavaScript?

Answer 11

It is an implicit parameter of all JavaScript functions. The value of this is determined by how a function is called.

Question 12

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

Answer 12

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 13

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

Answer 13

Call time

Question 14

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 14

window until we call it then it will be the character object

Question 15

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

character.greet();

Answer 15

It’s-a-me, Mario! Because our character object is responsible in calling the greet function.

Question 16

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

var hello = character.greet;
hello();

Answer 16

It’s-a-me, undefined! The hello function is not being called as a method of an object so it defaults to the window object, which does not have this.firstName so it is undefined.

Question 17

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

Answer 17

You can until the function is called.

Question 18

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

Answer 18

Looks to the object to the left of the dot or it defaults to the global window object.

Question 19

What kind of inheritance does the JavaScript programming language use?

Answer 19

Prototype-based inheritance or prototypal

Question 20

What is a prototype in JavaScript?

Answer 20

Prototypes are the mechanism by which JavaScript objects inherit features from one another.

Question 21

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 21

Those methods are defined on a “prototype” object and simply borrow those methods when they are needed.

Question 22

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

Answer 22

Looks in the object’s prototype chain

Question 23

What does the new operator do?

Answer 23

The new operator lets developers create an instance of a user-defined object type or of one of the built-in object types that has a constructor function.

It can create a new object with the formats of an object that has a constructor function.

Question 24

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

Answer 24

Prototype

Question 25

What does the instanceof operator do?

Answer 25

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

Question 26

What is a “callback” function?

Answer 26

A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action.

Question 27

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 27

setTimeout() method

Question 28

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

Answer 28

setInterval() method

Question 29

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

Answer 29

0

Question 30

What do setTimeout() and setInterval() return?

Answer 30

They both return a numeric ID value that identifies the timer created and can be used to cancel the timer.

Question 31

What is a client?

Answer 31

The clients are the ones who request a service. They are either a laptop, computer, or smartphone

Question 32

What is a server?

Answer 32

A computer that provides the network resources and provides service to other computers when they request it

Question 33

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

Answer 33

GET method

Question 34

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

Answer 34

http, an http method (get, put, post), the absolute URL

Question 35

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

Answer 35

The protocol version (HTTP/1.1), a status code either 200, 404, 302, and a status text

Question 36

What are HTTP headers?

Answer 36

HTTP headers let the client and the server pass additional information with an HTTP request or response. An HTTP header consists of its case-insensitive name followed by a colon (:), then by its value

Question 37

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

Answer 37

MDN

Question 38

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

Answer 38

NO, it is a optional but it is commonly used.

Question 39

What is AJAX?

Answer 39

AJAX allows you to collect data to update parts of the DOM of an HTML page without the need for a full page refresh.

Question 40

What does the AJAX acronym stand for?

Answer 40

Asynchronous JavaScript And XML

Question 41

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

Answer 41

XMLHttpRequest

Question 42

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

Answer 42

load event

Question 43

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

Answer 43

Prototypal inheritance