Background
The following is my first blog to achieve 8k+ view and 1st in Google SERP rank. However, it has some concerns and I decided to rewrite it.
In this article, I used global socket variable to manage socket events in a React app. Like the following:
// service/socket.js
export const socket = socketio.connect(SOCKET_URL);
// elsewhere
import {socket} from "service/socket";
However, fellow devs recommended to use React context API in their comments. And I began to think that using global variable is not a React-way either. (Although I believe that works too. Because socket does not change its state).
I updated my previous article, but I think it needs more explanation. So I decided to write an article that shows how to use React context API to manage one global socket instance.
1. Create Socket Context
We will use useContext hook to provide SocketContext to entire app.
Create a file in context/socket.js:
import socketio from "socket.io-client";
import { SOCKET_URL } from "config";
export const socket = socketio.connect(SOCKET_URL);
export const SocketContext = React.createContext();
2. Use socket context and provide a value
Add SocketContext provider at the root of your project or at the largest scope where socket is used:
import {SocketContext, socket} from 'context/socket';
import Child from 'components/Child';
const App = () => {
return (
<SocketContext.Provider value={socket}>
<Child />
<Child />
...
</SocketContext.Provider
);
};
3. Now you can use socket in any child component
For example, in GrandChild component, you can use socket like this:
import React, {useState, useContext, useCallback, useEffect} from 'react';
import {SocketContext} from 'context/socket';
const GrandChild = ({userId}) => {
const socket = useContext(SocketContext);
const [joined, setJoined] = useState(false);
const handleInviteAccepted = useCallback(() => {
setJoined(true);
}, []);
const handleJoinChat = useCallback(() => {
socket.emit("SEND_JOIN_REQUEST");
}, []);
useEffect(() => {
// as soon as the component is mounted, do the following tasks:
// emit USER_ONLINE event
socket.emit("USER_ONLINE", userId);
// subscribe to socket events
socket.on("JOIN_REQUEST_ACCEPTED", handleInviteAccepted);
return () => {
// before the component is destroyed
// unbind all event handlers used in this component
socket.off("JOIN_REQUEST_ACCEPTED", handleInviteAccepted);
};
}, [socket, userId, handleInviteAccepted]);
return (
<div>
{ joined ? (
<p>Click the button to send a request to join chat!</p>
) : (
<p>Congratulations! You are accepted to join chat!</p>
) }
<button onClick={handleJoinChat}>
Join Chat
</button>
</div>
);
};
OK, here are some explanations:
What is useContext?
-
useContextprovides a React way to use global state - You can use context in any child component
- Context values are states. React notices their change and triggers re-render.
What is useCallback? Why did you put every handlers inside useCallback?
-
useCallbackprevents reassigning whenever there is state update - Functions will be reassigned only when elements in the second argument are updated
- Since we passed an empty array to second argument, functions are assigned for only once
- You may forget (or don't bother) to use
useCallback. But you may face serious performance issues if there are many states and components in your project
What is useEffect and that [socket] array provided as the second argument?
The second argument is called dependency array. React will watch dependency array elements and whenever one of them is updated, the first argument function will be executed.
If you omit dependency array in
useEffect, the function will be executed whenever there is a state update.If the dependency array is an empty array, the function will be executed only once.
In React functional component, you can write
componentDidMountandcomponentWillUnmountalternatives in the following way:
useEffect(() => {
// here is componentDidMount
return () => {
// here is componentWillUnmount
}
}, []);
- It is strongly recommended to put every state that's used in the first argument function to the dependency array.
BONUS
If you want to use JWT token to authenticate socket connections, you can do like the following:
const getSocket = () => {
const token = getAuthToken(); // get jwt token from local storage or cookie
if (token) {
return socketio.connect(SOCKET_URL, {
query: { token }
});
}
return socketio.connect(SOCKET_URL);
};
Then in socket server, you can get jwt token like the following:
import SocketIO from "socket.io";
const io = new SocketIO.Server(expressApp);
const jwtMiddleware = (socket, next) => {
const {token} = socket.handshake.query;
// verify token
};
io.use(jwtMiddleware);
Discussion (12)
I have learned about ReactJS and Socket recently and written an video call and chat app using ReactJS and Socket .Here is my source code: github.com/lethanhvietctt5/video-c.... I hope it can help you guys to build a video chat app.
I don't think it's good approach. It will work for very small projects, but for larger ones not so much. Mixing socket communication with React will become overwhelming as app will grow, because all of it will spread through entire project. I would separate data source from frontend components. Imho better method is to extract actions and datasource to another files and provide only api to front components (as react-redux does). It would provide flexibility. Especially when you need to access different data sources (ie. local storage + cookie + websocket + ajax). React shouldn't "care" about where data comes from, business logic or communication with server.
Great article! Could you show how to implement 'user is typing indicator' with react? It seems when you keep track of a keyPress using a setTimeout you get a call to a function that sets a variable for every keyPress. I can share a code example somewhere if you want to discuss :)
Thanks! If you want to ask me anything, please open a stackoverflow post and share the link. I'm more than happy to help there :)
Elswhere in react on that way doesnt work,we can have only one instance of socket on client.
Good example. Thanks
I don't understand the JWT part. It's not written in relation to context. I have my app with a callback that is receiving the jwt on login then storing in storage which is when I want to connect to the socket, but I'm not too sure how to pass that jwt to context or force it to update when the jwt is available.
@bravemaster619
It is greate article, Thank you!
When the server
emitit sends some values. How we can access these values inuseCallback?Nice tutuorial. In my VS CODE console, I keep getting multiple request with polling, but it never does a a handshake with the server, what could be wrong?
And for initialize and listen of the events of the socket, it is better to use different useEffect hooks separately.
how do you globalize the socket instanse? ,,, so that i can call emits and listen to them in other modules of the project.
How to handle when client disconnected from server.