Microservices

Microservices in relation to React JS is a term used to describe a specific design pattern of developing applications. The microservice architecture is a method by which a single application is divided into a collection of smaller services, each running in its own process and communicating with each other through simple mechanisms, often an HTTP-based API.

This architecture allows individual microservices to be independently developed, deployed, and scaled. Each service can also be written in different programming languages and they can use different data storage technologies.

React JS is typically used to build user interfaces, hence it can be used to develop the client-side microservice which communicates with other server-side microservices.

Here's an example of this design pattern:

Assume you have a shopping app built with microservice architecture. The different functionalities of the app like user-authentication, product-catalog management, order management, payment gateway are all individual microservices.

If the user-authentication microservice is developed with React, it will handle just the user login/logout actions and upon successful authentication, it can communicate the user details to other services.

Here is a simple code snippet to demonstrate the user-authentication microservice with React.

```React
import React, {useState} from 'react';
import axios from 'axios';

const AuthenticationService= () => {
const [username, setUsername] = useState('');
const [password, setPassword] = useState('');

const handleSubmit = (event) => {
event.preventDefault();
axios.post('/api/authenticate', { // This '/api/authenticate' would be the API exposed by the server-side authentication microservice.
username,
password,
})
.then(response => {
// handle success
console.log(response);
})
.catch(error => {
// handle error
console.log(error);
})
}

// This form would be the user interface for the authentication service.
return (
<form onSubmit={handleSubmit}>
<label>
Username:
<input type="text" name="username" onChange={event => setUsername(event.target.value)} />
</label>
<label>
Password:
<input type="password" name="password" onChange={event => setPassword(event.target.value)} />
</label>
<button type="submit">Login</button>
</form>
);
}
export default AuthenticationService;
```

Each of the other functionalities would follow a similar pattern, and each would be a standalone application that can operate independently of the others. This allows for increased scalability, as in periods of high demand, you can simply deploy more instances of the specific microservice dealing with that demand. It also increases your apps resistance against faults, as failing in one area will not necessarily crash the whole application.