OOP

Question 1

What is a method?

Answer 1

A function which is a property of an object that can either be instance or static methods.

*Instance methods are built-in tasks performed by an object instance. Static methods are tasks called directly on an object constructor.

Question 2

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

Answer 2

A method definition uses the “function” keyword followed by a function code block that describes the method.

A method call uses the method name of its respective object followed by parenthesis and arguments (if any).

Question 3

Describe method definition syntax (structure).

Answer 3

The property name and a colon followed by the function keyword, parameters (if any), and the function code block.

Question 4

Describe method call syntax (structure).

Answer 4

The object name and method separated by the dot notation followed by parenthesis with arguments (if any).

Question 5

How is a method different from any other function?

Answer 5

Methods can be accessed through its object. Normal functions can be accessed anywhere.

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, and Polymorphism.

Question 8

What is “abstraction”?

Answer 8

The process of working with complex things in simple ways.

(i,e,. a light switch or automatic transmission.)

Question 9

What does API stand for?

Answer 9

Application Programming Interface

Question 10

What is the purpose of an API?

Answer 10

An API allows two or more computer programs to communicate with each other.

Question 11

What is this in JavaScript?

Answer 11

This is a variable that its value is determined by when a function is called.

Question 12

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

Answer 12

Implicit parameters can be understood from something else without being explained.

Question 13

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

Answer 13

The value is determined by when the functioned is called.

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 nothing because the function is not called.

Question 15

character.greet();

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

Answer 15

The string, It’s-a-me-Mario! because the this keyword refers to what is left of the dot which is the character object that has the firstName property.

Question 16

var hello = character.greet;
hello();

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

Answer 16

The result is undefined because hello(); is equivalent to window.hello in which hello is not a property of window.

Question 17

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

Answer 17

You cannot tell what the value of this would be in function or method definitions.

Question 18

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

Answer 18

Whatever is to the left of the dot. If there is no dot, then it is window.

Question 19

What kind of inheritance does the JavaScript programming language use?

Answer 19

JavaScript uses prototype-based (or prototypal) inheritance. (JavaScript objects give certain behaviors (methods) or data (properties) to other objects.)

Question 20

What is a prototype in JavaScript?

Answer 20

An object that contains properties and methods that can be used by other objects.

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 methods being called are defined on a separate prototype object.

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

The prototype object that the object is set to.

Question 23

What does the new operator do?

Answer 23

When a function is called with the new keyword, the function will be used as a constructor. New will do the following:

1. Creates a blank object.
2. Points the prototype property of the created instance to the prototype property of the constructor.
3. Runs the function (constructor) code block and makes the created instance (object) “this”.
4. Returns an expression or the new object.

Question 24

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

Answer 24

The .prototype property.

Question 25

What does the instanceof operator do?

Answer 25

It tests to see whether the prototype property of a constructor appears anywhere in the prototype chain of an object. The return value is either true or false.