SOLID PRINCIPLES IN JAVASCRIPT: WHAT THEY ARE, WHY YOU SHOULD USE THEM, AND HOW TO IMPLEMENT THEM
Tags: javascript, webdev, beginners, programming
Published: 2022-07-23 19:52:07

Software development has evolved rapidly in the past few years, and with it comes new paradigms for writing code. These principles are not just useful for making software easier to read and understand; they also make it more maintainable and extendable. If you’re a developer working on JavaScript projects, you’ve probably heard about the importance of following the SOLID principles. These principles not only help to organize your code appropriately, but also reduce coupling between classes and unwanted dependencies. In this blog post, we’ll look at what each of these principles is, why you should use them, and how you can implement them in your programming projects.

## What are SOLID principles?
SOLID stands for “solid” principles. These are five principles of software design that help to organize your code in a more maintainable and extensible way, as well as facilitate unit testing. The five SOLID principles are: 

- Single responsibility principle (SRP)
- Open-Closed Principle (OCP)
- Liskov substitution principle (LSP)
- Interface segregation principle (IP)
- Dependency inversion (DIP) & don’t break the chain (DBTC)

### Single responsibility principle (SRP)
The single responsibility principle states that every module or class should have one and only one purpose, and that responsibility should be entirely encapsulated inside of the module. The SRP is one of the most important SOLID principles, since breaking it often leads to software with higher coupling. The most important thing about this principle is to ask yourself, "What is the one and only thing this module or class is responsible for?" To break the single responsibility principle, a class or module would have to have more than one responsibility. For example, let’s say that we have a module that handles all our data. This module has functions that both query and store data. By following the SRP, we would create two modules: one that handles data input and another that handles data output.

### SRP in JavaScript: Why and how to use it
The SRP is a principle that many people struggle with when first implementing it. However, breaking the SRP can create issues in your code that might seem difficult to track down. As mentioned above, the SRP states that every module or class should have one and only one purpose. This means that each module or class should only be responsible for doing one thing, and nothing else. This helps to decrease coupling, which allows for easier extensibility and maintainability. If you’re working with a large team, it can be difficult to ensure that each module or class follows the SRP. If one person follows the principle and another doesn’t, it can create confusion and make it difficult to follow the code. However, there are a few things that you can do to help keep your code organized and adhere to this principle. The first thing would be to always ask yourself, "Is this module or class doing one thing?" If you find that it’s doing more than one, you can break it into smaller and more manageable pieces. Another thing you can do if you’re working with a team is to sit down with your teammates from time to time and ask them if their modules or classes follow the SRP. It’s also important to keep in mind that different programming languages, frameworks, and libraries have different conventions for naming classes and modules. You may find that your code breaks the SRP simply because of the way you’ve named your modules and classes.

#### SRP with react: Why and how to use it
React is a popular front-end development framework that uses components as building blocks for creating applications. Components function as modules and are used to create modular and reusable chunks of code that can be combined in different ways. This makes it easier to break down the code into modules that follow the single responsibility principle. If you decide to follow the SRP when creating your react components, you will create components whose only responsibility is to display some information. You wouldn’t have a single component that handles both the display of information and data fetching. This would help to break down the code into smaller and more manageable pieces, which would help to follow the SRP.

#### SRP with react and Redux : Why and how to use it
If you’re using a state management library such as Redux, you may be tempted to store all your data in the store. However, the store should only contain data that can be retrieved and displayed. This means that you shouldn’t store information that is only used to update the state of the application. Instead, you would create action creators that are responsible for transforming data from one state to another. This helps to follow the single responsibility principle since action creators have only one purpose; transform data from one state to another.

###Open-Closed Principle 
The Open-Closed Principle is a design principle that states that software should be open for extension and closed for modification. The principle was popularized by Eric Meyer in his book, Object-Oriented Design: A Systems Approach. In short, the goal of the Open-Closed Principle is to ensure that software is extensible but not modifiable. This means that an application should be able to expose functionality through its API (Application Programming Interface), but it should not be possible for users to change or modify the code behind that functionality. By adhering to this principle, you can ensure that your applications are easy to maintain over time and are well-suited for integration with other applications or services. One of the main benefits of adhering to the Open-Closed Principle is that it can help prevent bugs from creeping into your system. If you tightly guard your APIs, users will be unable to add their own features or customizations without causing problems for you.

### Liskov Substitution Principle (LSP)
The Liskov Substitution Principle (LSP) is a principle of object-oriented programming that states, “Any object that can be used in place of any other object should be assignable to the other object.” This means if you want to change the content of an object, it must be possible to do so without breaking the behavior of any other object. If an author wants to change the content of one of their objects, they first need to make sure that it is possible to do so without breaking the behavior of any other objects. If this cannot be guaranteed, then they should consider whether it is worth changing the content at all and instead refactor the code.

In JavaScript, this principle can be stated as: “You should not assume that any JavaScript object is interchangeable with any other JavaScript object.”

### Interface segregation principle (IP)
The interface segregation principle states that unrelated modules and classes should be kept separate from each other. This means that each module or class should only have access to the pieces of data that it needs in order to do its job. This helps to avoid coupling, which is especially important when working with third-party libraries. For example, if you have a third-party library that helps you with data visualization, you wouldn’t want to have that library’s code imported into your data retrieval module. This would cause a coupling between the two modules, which would make it difficult to make changes to both modules since they would rely on each other. By following the IP, you would keep the two modules separate, which would make it easier to make changes and break the coupling between the two modules.

### Dependency inversion (DIP)
The dependency inversion principle states that the code should depend on abstractions instead of concrete implementations. This means that a module or class should use a function or an interface that returns an instance of that function or interface. An example of this would be a module that retrieves and stores data from a database. That module should only use an interface such as an ORM module to retrieve data from the database. This would allow that module to be used with any database because it doesn’t depend on a concrete implementation.

#### DIP with ES6 Classes
JavaScript uses the class keyword to define classes and the new keyword to create instances from those classes. Classes are used to create objects that can be customized. Following the DIP with ES6 classes would mean that each class only uses the class keyword and doesn’t use the new keyword. This would allow each class to be used independently as an abstraction.

### Don’t break the chain (DBTC)
The DBTC principle is the last of the SOLID principles. This principle states that every link in a chain should be strong enough to sustain the weight of the chain. This means that every single link in your code should be well-written and adhere to the SOLID principles. This would ensure that the entire codebase follows the SOLID principles and would be easy to read and maintain.