JavaScript Design Patterns: The Factory Pattern

Arthur Frank
May 14 · 6 min read
Photo by Matteo Catanese on Unsplash

Quick intro

This is the second article in JavaScript Design Patterns series, where I explain Design Patterns with simple words. There is a ton of information out there on the internet, which is incredibly confusing, dry and boring. My goal is to explain complex things in a simple and enjoyable manner.

Previously we have covered Adapter Design Pattern, which you can read about here.

This time we are going to dive into Factory Pattern and how to make use of it in JavaScript.

Problem to solve

Photo by Ross Sneddon on Unsplash

Imagine a project, where you have to access complex Data from various sources like Data Bases, APIs, file uploads etc. All that information has to be consumed and used by your application code.

In most cases you will be operating with objects. As you probably know is an incredibly simple Object Type. Therefore, if we just use Raw JSON in our application, we are exposing our code to a variety of issues.

#1 Object Structure

We are not in control of the structure of these objects. If we are going to use these objects as we receive them, we are adding risk to our code to break in multiple places, if data properties will change. Good example might be, if an API data source has changed its response object or someone renamed a column in Data Base, this will change the structure of the object your code receives.


Code Sample by Arthur Frank
Code Sample by Arthur Frank

This will lead to a broken code and bugs in multiple places, due to wrong properties being used.

#2 Codebase Consistency

We are exposing our code to a huge inconsistency. If you receive similar data, like for example object from more than one source, there is a chance, that two same books may look different from an Object perspective.


Code Sample by Arthur Frank
Code Sample by Arthur Frank

General idea is that, we are not in control of our Domains. But the opposite, we are led by outside data structures. So instead of building an application around your own data implementation you will be building you implementation around data structures dictated by outside sources.

This issue is quite big, because it takes over your codebase conventions and standards.

#3 Object Type

We are unable to confirm which object type we are operating with at a particular point in time. For example, we may end-up with using Book Object as User or a Blog Post object.


Code Sample by Arthur Frank

As you can see from the example above, we are not able to determine to which instance each JSON object belongs.

Factory Pattern in JavaScript

Photo by Alexander Tsang on Unsplash

Principal of Factory Pattern is incredibly simple in its core. This pattern is categorised as Creational, and there is a reason for that. Factory is designed to create. And when we speak about programming, we want it to create Objects, which follow our Domain conventions.

As we know JavaScript application can be written in many ways, like for example Functional or semi OOP style. Therefore, I think it’s fair to say, that there are potentially multiple ways to implement Factory Pattern.

Though as I said in my previous article about Adapter Pattern, the KEY here is the concept itself, which can make our code cleaner and more robust, not an exact 1:1 implementation from a book.

Factory Pattern — simple diagram

This is how we can visualise our codebase consuming and handling data without Factory Pattern. As you can see everything is leaking to our main codebase in a Raw state, with potentially small tweaks and transformations.

Diagram without Factory by Arthur Frank

On the diagram below we can see a simple visualisation of how situation changes if we are using Factory Pattern where it’s appropriate.

Diagram with Factory by Arthur Frank

Factory Pattern — code example

Hopefully you are having a solid idea of Factory Pattern benefits and what is the general idea behind it. Now let’s see, how you can implement it in JavaScript application.

Let’s imagine a small application, with this structure.

We have simple entry point and area where we have our own definitions of objects we want to manipulate within our code.

A simple example of the Book Domain Object may look like this:

Code Sample by Arthur Frank

Bear in mind these code samples are massively simplified. In case of the Book Domain Object, we have a simple with three properties — , , which WE define, and we can be 100% sure they will never change.

Now, let’s see the Factory:

Code Sample by Arthur Frank

As you can see its really simple which also can be a really if you are in completely functional programming paradigm. The last step is to use our Factory.

Code Sample by Arthur Frank

And this is it! This is how simple the pattern is. Let see also what other benefits it gives us now.

Code Sample by Arthur Frank

As you can see intellisense is now assisting us with available properties and methods from our Domain Object.

We are 100% sure, that structure will be same for all instances of the Book Object we create from various sources including our own code — for example if we decide to create completely new Book Object.

We also can see the actual type of the Object we are operating right now.

Code Sample by Arthur Frank

And we can see an instance of which class we are working with. This is giving us some sort of a Type control — you can build more robust code with better Unit Test and validation of data you are using.

Code Sample by Arthur Frank

Quick, one sentence summary.

Factory creates Domain Objects, from fragile or vulnerable data structures.


Photo by Kelly Sikkema on Unsplash

Thank you for taking time and reading this article. I really hope, you have gained some good insights and became even better engineer.
Have a great time, do things you love and see you in the next post. 🔥

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