Object-oriented programming

Question 1

What is a method?

Answer 1

A method is a function which is a property of an object.
In JavaScript functions themselves are objects, so, in that context, a method is actually an object reference to a function.

Question 2

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

Answer 2

o Method definitions will always have a function keyword and a code block
o Method calls start with an object name and has arguments that are being passed

Question 3

Describe method definition syntax (structure).

Answer 3

propertyName: functionName( ) {
Return ‘anything’;
}

Question 4

Describe method call syntax (structure).

Answer 4

objectName.method( )

Question 5

How is a method different from any other function?

Answer 5

They are functions stored in an object

Question 6

What is the defining characteristic of Object-Oriented Programming?

Answer 6

Objects can contain both:

• Data (as properties)
• Behavior (as methods)

Question 7

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

Answer 7

o Abstraction
o Encapsulation
o Inheritance
o Polymorphism

Question 8

What is “abstraction”?

Answer 8

Being able to work with (possibly) complex things in simple ways (such as, turning a light on/off)

Question 9

What does API stand for?

Answer 9

Application Programming Interface

Question 10

What is the purpose of an API?

Answer 10

Give programmers a way to interact with a system(s) in a simplified, consistent fashion (aka abstraction) without knowing about how they all work independently.

Question 11

What is ‘this’ in JavaScript?

Answer 11

The object that you’re working within

Question 12

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

Answer 12

The parameter is available (in a function’s code block) even though it was never included in the function’s parameter list OR declared in a 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

Undefined (there is nothing in front of greet)

Question 15

Given this character object:

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

What is the result of the following code snippet? Why?
character.greet();

Answer 15

It’s a me, Mario! Because greet is being called on the character object

Question 16

Given this character object:

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

What is the result of the following code snippet? Why?
var hello = character.greet;
hello();

Answer 16

It’s a me, undefined!

Because ‘this’ is being called from the window object and not the character object

Question 17

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

Answer 17

There is no way to know in a definition because there is no value yet

Question 18

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

Answer 18

By checking the object left of the dot

Question 19

What kind of inheritance does the JavaScript programming language use?

Answer 19

Prototype-based (prototypal) inheritance

Question 20

What is a prototype in JavaScript?

Answer 20

Object with properties and methods that can be reused

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

Via inheritance from the prototypes (prototypal inheritance)

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

its prototype (starts from the nearest prototype and moves up until it finds what it needs)