<p>WebSockets are great. They provide a bi-directional, real-time data flow between the server and the client. This connection can often be an elegant solution when one needs a constant stream of data to/from the server. There's a whole host of everyday use cases, one of which will I will explore here.</p>

<h1>CKC Management</h1>
<p>Here at CKC, we have an unofficial, somewhat-hobby project that we work on sporadically. The app is a project management tool that is still in quite a premature phase, but it is an excellent excuse for us to delve into the world of WebSockets. One of the main features as of now is a Kanban board. WebSockets pair quite seamlessly with Kanban boards. They allow multiple users to edit the board unanimously while keeping all users up to date in real-time.</p>
<hr>
<p>There are several techniques to wield the power of WebSockets. The method we chose for this project is relatively simple: we use a standard REST API to make changes on the backend, then we send a message through to the WebSocket to indicate what data has changed. Furthermore, to make changes, we can call a PATCH/PUT/POST method to the API, and once that resolves, we send a message up to the WebSocket. We then forward the message to the other clients that are listening. To reiterate, the message dictates what data needs updating. So once a client receives a message from it's WebSocket connection, it triggers a GET request to fetch the newly updated data. This is not the typical way to set up a WebSocket and has its cons. It would be more efficient and responsive for the client to send/receive data straight through the socket's connection instead of pairing it with a REST architecture. While we may change this in the future, we were going for simplicity in this initial stage.</p>
<h1>Let's get to work</h1>
<p>I recently implemented our existing WebSocket for CKC Management into a barebones React Native app. Our web app is built with Vue.js, but I'll be going over the React Native implementation. We are assuming that you already have a backend running at this point; I will not be covering that.</p>
<p>This process is relatively straightforward, but I will assume you have a React Native project up and running at this point. If you're unsure on how to get started with React Native, you can refer <a href="https://itnext.io/set-up-react-native-with-expo-1e63a82d01ac">to this guide</a>.</p>
<p>To start, we need to initialize the connection to our WebSocket:</p>
<pre><code class="language-js">...

const ws = new WebSocket("&#x3C;websocket_endpoint>")

...
</code></pre>
<p>Next, we need to add an event listener to this connection in the app's top level component. To initialize this listener once when the app loads and never again, we can utilize React's <code>useEffect</code> hook. <code>useEffect</code> is handy here because we need to set up this event listener when the app first loads rather than reinitializing it every render:</p>
<pre><code class="language-js">const ws = new WebSocket("&#x3C;websocket_endpoint>")


function App() {
    ...
    
    useEffect(() => {
            // This fire's when the component mounts
            ws.onmessage = handleWsMessage
    }, [])
    
    ...
}


</code></pre>
<p>Now that we have the event listener up and running, our function, <code>handleWsMessage</code>, will fire every time something comes through our socket. If you recall, we will receive a simple message and make some API calls based on that message. Our function, <code>handleWsMessage</code>, will handle this message and decide how to proceed. In this case, we'll just run a simple GET request to our API whenever we receive a message that indicates new data exists on the server. To keep things simple for now, we'll read down data and not write any message back up to the socket. Our web app will do the writing for now. Our GET request will fetch data, and then we can store that data in our state variable <code>tasks</code>:</p>
<pre><code class="language-js">...

const [tasks, setTasks] = useState([])

const fetchTasks = async () => {
    const tasks = await getTasks() // our GET request

    setTasks(tasks)
}

const handleWsMessage = async (message) => {
    let message_obj = JSON.parse(message.data)

    if (message_obj.type === 'task_update') {
        await fetchTasks()
    }
}

useEffect(() => {
    // This fire's when the component mounts
    ws.onmessage = handleWsMessage
}, [])

...
</code></pre>
<p>So we've done it! We are listening to our WebSocket and then fetching changes accordingly. All we have left is to render this to the page:</p>
<h1>Let's see it in action:</h1>
<p>On the left, we have a Vue.js web app and, on the right, is our React Native app. Both are communicating with the same backend and WebSocket.</p>
<div>
    <img src="/assets/blog/2020-11-22/websocket-example.gif">
</div>
<p>And there you have it: an entry-level approach to working with WebSockets. These can be quite powerful, and I encourage you to experiment with them. Think about how a WebSocket connection could take your project to the next level!</p>
<h2>Full Example</h2>
<p>I've added a bit more code to clean things up a bit.</p>
<pre><code class="language-jsx">import React, { useEffect, useState } from 'react';
import styled from 'styled-components'
import { View } from 'react-native';
import { Header } from 'react-native-elements'

// components
import Task from "./Task";

//utils
import { getTasks } from "./utils";

//websocket connection
const ws = new WebSocket("ws://localhost/dashboard")

function App() {
    const [tasks, setTasks] = useState([])

    const fetchTasks = async () => {
        const tasks = await getTasks() // our GET request
        setTasks(tasks)
    }

    const handleWsMessage = async (message) => {
        let message_obj = JSON.parse(message.data)
        if (message_obj.type === 'task_update') {
            await fetchTasks()
        }
    }

    useEffect( () => {
        // This fires when the component mounts
        ws.onmessage = handleWsMessage

        async function getTasks() {
            // This allows us to use async inside useEffect
            await fetchTasks()
        }
        getTasks()

        // cleans up the useEffect hook
        return getTasks
    }, [])

    return (
        &#x3C;Container>
            {
                tasks.map((task, i)=>{
                    return (
                        &#x3C;Task key={i} task={task}/>
                    )
                })
            }
        &#x3C;/Container>
    );
}

export default App


// Simple styled-component usage
const Container = styled.View` 
  justify-content: center;
  align-content: center;
`


</code></pre>

Websockets and the Frontend