4/11 - 4/15/2022

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

The definition is in the ‘value’ position of an object, after the property. It starts with the ‘function’ keyword.
The method call is done by typing the object’s name followed by the property with dot notation.

Question 3

Describe method definition syntax (structure).

Answer 3

cons obj = {
    firstName: Daniel,
    lastName: Cho,
    fullName: function () {
        return this.firstName + " " + this.lastName;
    }
};

The “function()” after “fullName” is an example of method definition syntax.

Question 4

Describe method call syntax (structure).

Answer 4

Referring to last card, an example of a method call syntax would be obj.fullName();

Question 5

How is a method different from any other function?

Answer 5

A function is a set of instructions that perform a task.

A method is a set of instructions that are associated with an object.

Question 6

What is the defining characteristic of Object-Oriented Programming?

Answer 6

The defining characteristic of OOP is that objects can contain both data (as properties) and behavior (as methods).

Question 7

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

Answer 7

1. Abstraction
2. Encapsulation
3. Inheritance
4. Polymorphism

Question 8

What is “abstraction”?

Answer 8

Being able to work with 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

To give programmers a way to interact with a system in a simplified, consistent fashion: aka, an abstraction.

Question 11

What is ‘this’ in JavaScript?

Answer 11

‘this’ is an implicit parameter and its value is determined when the function is called. If the function is called by itself (not as a method of an object), the value of ‘this’ is the global window object. When the function is assigned as a method of an object, the value of ‘this’ is the object. If you cannot see where the function (or method) is called, you cannot say for sure what the value of ‘this’ is.

Question 12

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

Answer 12

To say that ‘this’ is an ‘implicit parameter’ means 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 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

‘this’ refers to the object ‘character’. ‘this.firstName’ refers to ‘character.firstName’.

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 ‘this’ is used in a function that is a method of an object.

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!’

This is the result of the code snippet because you cannot see where the method (character.greet) is being called.

Question 17

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

Answer 17

You can’t. The value of ‘this’ is determined when the function or method is called, not when it’s defined.

Question 18

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

Answer 18

You can tell what the value of ‘this’ will be for a particular function by checking to see if there is anything to the left of a dot preceding its name. If there isn’t anything, then the value of ‘this’ will be the global window object. For a method definition, the value of ‘this’ will be the object that is to the left of the dot.

Question 19

What kind of inheritance does the JavaScript programming language use?

Answer 19

Prototype-based (or prototypal) inheritance

Question 20

What is a prototype in JavaScript?

Answer 20

A prototype in JavaScript is an object that has methods and properties passed into it so other objects can access the prototype to perform tasks that those objects cannot perform themselves.

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

The strings, arrays, and numbers borrow those methods from their respective prototype objects where those methods are defined.

Question 22

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

Answer 22

In its prototype chain

Question 23

What does the ‘new’ operator do?

Answer 23

It creates an instance of a user-defined object type or of one of the built-in object types that has a constructor function.

Per MDN:

1. Creates a blank, plain JavaScript object.
2. Adds a 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 (i.e. all references to ‘this’ in the constructor function now refer to the object created in the first step).
4. Returns ‘this’ if the function doesn’t return an object.

Question 24

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

Answer 24

Function.prototype

Ex: function Car() {}
car1 = new Car();
car2 = new Car();

console.log(car1.color); // undefined

Car.prototype.color = ‘original color’;
console.log(car1.color); // ‘original color’

car1. color = ‘black’;
console. log(car1.color); // ‘black’

console. log(Object.getPrototypeOf(car1).color); // ‘original color’
console. log(Object.getPrototypeOf(car2).color); // ‘original color’
console. log(car1.color); // ‘black’
console. log(car2.color); // ‘original color’

Question 25

What does the ‘instanceof’ operator do?

Answer 25

‘instanceof’ tests to see if the ‘prototype’ property of a constructor appears anywhere in the prototype chain of an object.

Ex: function Car(make, model, year) {
  this.make = make;
  this.model = model;
  this.year = year;
}
const auto = new Car('Honda', 'Accord', 1998);

console.log(auto instanceof Car);
// expected output: true

console.log(auto instanceof Object);
// expected output: true

Ex.2: // defining constructors
function C() {}
function D() {}

let o = new C()

// true, because: Object.getPrototypeOf(o) === C.prototype
o instanceof C

// false, because D.prototype is nowhere in o's prototype chain
o instanceof D

o instanceof Object // true, because:
C.prototype instanceof Object // true

C.prototype = {}
let o2 = new C()

o2 instanceof C // true

// false, because C.prototype is nowhere in
// o's prototype chain anymore
o instanceof C

D.prototype = new C()  // add C to [[Prototype]] linkage of D
let o3 = new D()
o3 instanceof D        // true
o3 instanceof C        // true since C.prototype is now in o3's prototype chain

Question 26

What is a client?

Answer 26

The service requester in the client-server model. The client requests services from the server, such as getting resources from the server or pushing data to the server

Question 27

What is a server?

Answer 27

Providers of a resource or services in the client-server model. A couple of the forms a server can take is a web server or a file server.

Question 28

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

Answer 28

An HTTP GET request

Question 29

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

Answer 29

1. An HTTP method (GET, PUT, or POST)
2. The request target, usually a URL or the absolute path of the protocol, port, and domain are usually characterized by the request context.
3. The HTTP version

Question 30

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

Answer 30

1. The protocol version, usually HTTP/1.1
2. A status code, indicating success or failure of the request. Common status codes are 200, 404, or 302.
3. A status text. A brief, purely informational, textual description of the status code to help a human understand the HTTP message.

Question 31

What are HTTP headers?

Answer 31

HTTP headers are one line of code messages that allow the client and server to send additional information to each other.

Headers allow you to add more information for a request.

Question 32

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

Answer 32

MDN

Question 33

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

Answer 33

No

Question 34

What is a “callback” function?

Answer 34

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

Question 35

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 35

The global setTimeout() function

Question 36

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

Answer 36

The setInterval() function

Question 37

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

Answer 37

0 ms

Question 38

What do setTimeout() and setInterval() return?

Answer 38

A numeric, non-zero value which identifies the timer created by the call to setTimout() or setInterval().

The id that is used to cancel the interval or timeout.

Question 39

What is AJAX?

Answer 39

AJAX is a technique for loading data into part of a page without having to refresh the entire page.

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

The XMLHttpRequest constructor

Question 42

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

Answer 42

The ‘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

They are both part of the eventarget interface (i.e. inheritance).

And also because of the Object constructor