DEV Community: Glenn all

how to use react context?

Glenn all — Sun, 04 Dec 2022 12:01:08 +0000

React's Context API allows you to share values such as state or data between components without passing props down manually through every level of the component tree. This can be especially useful when you have some values that are needed by many components in your application.

To use the Context API, you first need to create a context using the createContext() method from the react package. This method returns an object with two components: Provider and Consumer.

import { createContext } from 'react';

const MyContext = createContext();

The Provider component is used to provide a value for the context, which can then be consumed by the Consumer component. The Provider component should be placed at the root of your component tree, wrapping the components that need access to the context value.

import MyContext from './MyContext';

function App() {
  return (
    <MyContext.Provider value="Hello World">
      <MyComponent />
    </MyContext.Provider>
  );
}

In the example above, the value "Hello World" is provided for the MyContext context. This value can then be consumed by the MyComponent component, or any other component nested inside it, using the Consumer component.

import MyContext from './MyContext';

function MyComponent() {
  return (
    <MyContext.Consumer>
      {value => <p>{value}</p>}
    </MyContext.Consumer>
  );
}```



The Consumer component expects a function as its child, which will be called with the current context value. The function should return a React element that uses the context value. In the example above, the context value is used to render a p element with the value inside it.

You can also use the useContext() hook from the react package to consume the context value inside a functional component.



```js
import { useContext } from 'react';
import MyContext from './MyContext';

function MyComponent() {
  const value = useContext(MyContext);
  return <p>{value}</p>;
}

The useContext() hook takes the context object as its argument and returns the current context value. You can then use this value inside the component.

It's also possible to update the context value using the useState() hook inside a component that is a descendant of the Provider component. This can be useful for implementing state management using the Context API.

import { useContext, useState } from 'react';
import MyContext from './MyContext';

function MyComponent() {
  const [value, setValue] = useState(useContext(MyContext));

  function handleClick() {
    setValue('Hello World!');
  }

  return (
    <>
      <p>{value}</p>
      <button onClick={handleClick}>Update Value</button>
    </>
  );
}

In the example above, the context value is initially set to the value provided by the Provider component using the useContext() hook. A button element is then rendered with an onClick event handler that updates the value using the setValue() function from the useState() hook

what is service discovery? (example provided)

Glenn all — Sun, 04 Dec 2022 11:13:35 +0000

Service discovery is a process by which services that are available on a network are identified and located. This can be useful in distributed systems, where multiple services may be running on different machines and need to communicate with each other.

Service discovery typically involves the use of a discovery service, which maintains a list of available services and their locations on the network. Clients can query the discovery service to find the location of a specific service, and then connect to that service directly to access its functionality.

Service discovery tools

There are many tools that can be used to implement service discovery in a distributed system. Some common tools include:

Consul: Consul is a tool for service discovery and configuration management in distributed systems. It provides a simple and effective way to locate services and manage their configurations.

Zookeeper: Zookeeper is a distributed coordination service for distributed applications. It provides a centralized registry for services, allowing clients to discover and connect to the services they need.

Eureka: Eureka is a service registry for the Netflix OSS ecosystem. It provides a way for services to register themselves and for clients to discover and connect to the services they need.

etcd: etcd is a distributed key-value store that can be used for service discovery. Services can register themselves by storing their metadata in etcd, and clients can discover and connect to the services they need by querying etcd.

Kubernetes: Kubernetes is a container orchestration platform that provides built-in support for service discovery. Services can be registered with Kubernetes and accessed using DNS or an API, allowing for easy and efficient discovery and connectivity.

Here is an example of how service discovery might be implemented using** Express.js** and Consul:

// Register the service with Consul
consul.register({
  name: "service-name",
  port: 8080,
  check: {
    http: "http://localhost:8080/health",
    interval: "10s"
  }
});

// Create an Express.js app
const app = express();

// Register the service with Express.js
app.register("service-name", {
  port: 8080,
  check: {
    http: "http://localhost:8080/health",
    interval: "10s"
  }
});

// Start the Express.js app
app.listen(8080); ```

`

In this example, the service is registered with both Consul and Express.js, providing a way for clients to discover and connect to the service using either tool. Consul is also used to manage the service's configuration, allowing for dynamic updates without requiring a restart.

what is microservice architecture?

Glenn all — Sun, 04 Dec 2022 10:10:11 +0000

Microservice architecture is a design approach for building software systems that are composed of small, independent, and modular components, known as microservices.

Each microservice is designed to perform a specific function or set of related functions, and can be developed, deployed, and maintained independently of the other microservices in the system. This allows for flexibility, scalability, and resiliency, as the system can be easily adapted and evolved to meet changing requirements.

Example of microservice:

let's define a simple microservice that exposes a single endpoint /add which accepts two numbers as query parameters, a and b, and returns the result of adding them.

tech stack Express

const express = require('express');
const app = express();

// A simple function that adds two numbers
function add(a, b) {
  return a + b;
}

// Define an endpoint that accepts two numbers
// and returns the result of adding them
app.get('/add', (req, res) => {
  const a = parseInt(req.query.a);
  const b = parseInt(req.query.b);
  const result = add(a, b);
  res.send({result});
});

// Start the server on port 3000
app.listen(3000, () => {
  console.log('Microservice listening on port 3000!');
});

To run this microservice, you would need to install the required dependencies, such as Express, and then start the server by running the code. Once the server is running, you can send HTTP requests to the /add endpoint to test it out. For example, you could use the following curl command to send a request to add 2 and 3:

curl 'http://localhost:3000/add?a=2&b=3'

This would return the following response:

{"result":5}