JS and Object-Oriented Programming

Question 1

What is a method?

Answer 1

A function which is a property of an object.

Question 2

How is a method different from any other function?

Answer 2

It is associated with an object

Question 3

What is the defining characteristic of Object-Oriented Programming?

Answer 3

Related method and variables are bundled together in objects - a program is the interaction of the objects with each other

Question 4

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

Answer 4

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

Question 5

What is “abstraction”?

Answer 5

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

also: hiding/abstracting away the details of how something is implemented to make working with it easier

Question 6

What does API stand for?

Answer 6

application programming interface

Question 7

What is the purpose of an API?

Answer 7

An API allows programs/objects to interact with other programs/objects and controls what can be accessed or modified.

Question 8

What is the keyword ‘this’ in JavaScript?

Answer 8

A reference to the object that a method/function is related to/associated with;

Question 9

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

Answer 9

It means that even if ‘this’ isn’t listed as a parameter in the function/method definition, it is still defined and available to use inside the function/method

Question 10

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

Answer 10

Call-time;

Question 11

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

Answer 11

You can’t. The value of this is determined at call time (it is a call-time binding)

Question 12

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

Answer 12

Look at how/where the function/method is being called

– also check left of the dot

Question 13

What kind of inheritance does the JavaScript programming language use?

Answer 13

Prototypal inheritance / prototype-based inheritance

Question 14

What is a prototype in JavaScript?

Answer 14

a JavaScript prototype is an object that contains properties and methods that can be used by other objects.

Question 15

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 15

The methods have been inherited through prototypal inheritance

Question 16

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

Answer 16

Its prototype

Question 17

What does the ‘new’ operator do?

Answer 17

The keyword ‘new’ is used to initialize an instance of a constructor function.

What calling a function with ‘new’ keyword specifically does:

1. Creates an empty javascript object
2. Adds the __proto__ property to the object
3. Sets ‘this’ keyword to reference the object created in step 1
4. Returns ‘this’ object if the function doesn’t return an object.

Question 18

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

Answer 18

the prototype property

Question 19

What does the ‘instanceof’ operator do?

Answer 19

It is used to check if an object was made from another object (has the constructor somewhere in it’s prototype chain)