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SOLID is a set of principles. They are mainly guidelines for software professionals who care about their code quality and maintainability.

React is not object-oriented by nature, but the main ideas behind these principles can be helpful. In this article, I will try to demonstrate how we can apply these principles to write better code.

In a previous article, we talked about the single-responsibility principle. Today, we will discuss the second principle of SOLID: the Open-Closed principle.

What Is the Open-Closed Principle?

According to Thorben Janssen on Stackify:

“Robert C. Martin considered this principle as the ‘most important principle of object-oriented design.’ But he wasn’t the first one who defined it. Bertrand Meyer wrote about it in 1988 in his book Object-Oriented Software Construction. He explained the Open/Closed principle as:
‘Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification.’”

This principle tells you to write code in such a way that you will be able to add additional functionality without changing the existing code.

Let’s see where we can apply this principle.

Let’s Start With an Example

Say we have a User component where we pass a user's details and the main purpose of this class is to show the details of that particular user.

import React from 'react';

export const User = ({user}) => {

    return <>
        <div> Name: {user.name}</div>
        <div> Email: {user.email}</div>
    </>
}

This is simple enough to start with. But our life is not so simple. After a few days, our manager tells us that there are three types of users in our system: SuperAdmin, Admin, etc.

And each of them will have different information and functionalities.

A Bad Solution

Well, the first and obvious solution is to have a conditional inside our component and render different information based on the different user types.

import React from 'react';

export const User = ({user}) => {

    return <>
        <div> Name: {user.name}</div>
        <div> Email: {user.email}</div>
        {
            user.type === 'SUPER_ADMIN' &&
            <div> Details about super admin</div>
        }
        {
            user.type === 'ADMIN' &&
            <div> Details about admin</div>
        }
    </>
}

Do you see what’s wrong here?

Firstly, our code is messy now.

Secondly, what if we need another type of user? We would then need to go into User.js and add another condition for that particular type of user.

This is a clear violation of the Open-Closed principle because we are not allowed to alter the code inside the User component.

What’s The Solution?

OK, so there are two main techniques that we can apply in this scenario:

Higher-order component
Component composition

It’s better to go the second route whenever possible, but there can be cases where using a HOC is necessary.

For now, we will use a technique recommended by Facebook that is called the composition of components.

Let’s Create Separate User Components

Now we need to design our code in such a way that we don’t need to add a conditional inside the User.js component. Let’s create a separate component for SuperAdmin:

import React from 'react';
import {User} from "./User";

export const SuperAdmin = ({user}) => {

    return <>
        <User user={user} />
        <div> This is super admin user details</div>
    </>
}

Similarly, another one for Admin users:

import React from 'react';
import {User} from "./User";

export const Admin = ({user}) => {

    return <>
        <User user={user} />
        <div> This is admin user details</div>
    </>
}

And now our App.js file becomes

import React from 'react';
import Admin from './Admin'
import SuperAdmin from './SuperAdmin'


export default function App = () =>{

  const user = {}

  const userByTypes = {
    'admin' : <Admin /> ,
    'superadmin' : <SuperAdmin />
  }

  return <div>
    {userByTypes[`${user.type}`]}
  <div/>
}

Now we can create as many user types as we need. Our logic for particular users is encapsulated and we don’t need to revisit our code for any additional modifications.

Some might argue we are increasing the number of files unnecessarily.
Sure, you can leave it as-is for now, but you will definitely feel the pain as the complexity of the application grows.

Caution

SOLID is a set of principles. They are not mandatory for you to apply in every scenario. As a seasoned developer, you should find a good balance between code length and readability.

Don’t obsess too much over these principles. In fact, there is a famous phrase to explain these scenarios:

“Too Much SOLID.”

So knowing these principles is good, but you have to keep a balance. You may not need these compositions for one or two extra fields, but keeping them separate will definitely help in the long run.

Conclusion

Knowing these principles will take you a long way because at the end of the day, a good piece of code is what matters and there is no single way of doing things.

Have a great day!

Resources

https://stackify.com/solid-design-open-closed-principle/

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