Chapter 5 Overview

Object Oriented programming has become the predominant way of developing software today. While there are some people who believe that object-oriented programming (OOP) is a misstep, there are also people who quite dogmatic about OOP. Both of the Universities I have attended tend to favor the OOP approach but there is starting to be a look at the alternatives to OOP, with functional programming gaining traction. I am a bit more flexible when it comes to programming believing that methodologies, like languages, are tools and one should try and use the appropriate tool for the problem they are dealing with.

Object Oriented approaches are so common, however, that no matter what your stance on OOP is, you should at least be familiar with the concepts behind it. This section of the book takes a look at the core OOP features that JavaScript supports. Unfortunately, like a lot of things about JavaScript, things are not as straightforward as they should be. While JavaScript has always had support for Objects, the language itself did not explicitly support OOP constructs until the ECMAScript 6 standard was released. This means that older browsers do not support the new language keywords but there are a shrinking number of people who use those browsers. It also means that there is a lot of legacy code out there that does OOP the hard way. These techniques are still valid so it is wise to at least be familiar with them.

In this chapter we will look at a number of OOP related concepts looking at what the idea behind the concept is, how ECMAScript 6 supports that concept, and the "old" way of handling the concept.

To start with, in the "NameSpace" section we will be looking at the name space problem and how to get around it. Even if you are not into the other OOP concepts, name spaces are something that ALL non-trivial programs should use.

It goes without saying that objects are important to object-oriented programming so we will then revisit creating objects in "Creating Objects". This will be followed by "Constructing Classes". Classes are what most OOP languages use to define objects with a class keyword being something that was missing from JavaScript until the ECMAScript 6 standard was released.

One of the more powerful, albeit over-abused, features of object oriented programming is the use of inheritance. This allows you to create new classes based off of existing classes without needing to write most of the functionality and will explained in the "Inheritance" section. Polymorphism is how OOP languages take advantage of inheritance by letting you use a child class in place of a parent class. JavaScipt uses a variant of polymorphism known as Duck Typing which gives you a lot of flexibility and power but has some downsides. These issues will be covered in "Polymorphism and Duck Typing".

JavaScript handles classes a bit different from most other object oriented languages. This leads to a strange issue when trying to use an objects function as a call-back. This issue can be solved using something known as binding, which we will explain in a section strangely named "Binding".

What allows JavaScript to bind functions actually is a very powerful construct known as a closure. Closures are a bit confusing and you may not want to use them in your programs, but they are an important JavaScript technique so I will be covering them in the "Closures" section.

And that should cover all the object oriented JavaScript knowledge that you will need for the remainder of this book.