WebSocket is a network protocol that implements full duplex communication between browsers and servers. Compared with traditional polling methods, it has lower latency, less bandwidth consumption and stronger real-time performance. Its core advantages include: 1. Reduce latency: no need to establish frequent connections; 2. Reduce bandwidth usage: avoid duplicate HTTP header information; 3. Strong real-time: The server can actively push messages. The front-end realizes communication by creating WebSocket instances and listening to open, message, error, and close events; the back-end such as Node.js can use the ws library to build services. Pay attention to when using: 1. Handle connection failures and downgrade solutions; 2. Add an automatic reconnection mechanism; 3. Use wss encryption to ensure security; 4. Unified message format such as JSON. Rationally managing connections and exception handling is the key to stable operation.

WebSocket is a very practical tool in JavaScript real-time applications. It can establish a persistent connection between the browser and the server and realize two-way communication. Compared with the traditional polling method, WebSocket is more efficient and responsive, and is especially suitable for chat applications, real-time data updates and other scenarios.

What is WebSocket?

WebSocket is a network protocol that allows a persistent connection between the client and the server to communicate with full duplex (i.e. both parties can send and receive messages). This is different from HTTP request/response mode, where HTTP requires a new connection to be established for each request, while WebSocket requires only one handshake to communicate continuously.

The benefits of using WebSocket include:

• Lower latency: No frequent HTTP request overhead
• Less bandwidth consumption: no duplicate header information is required for each communication
• Strong real-time performance: the server can actively push messages to the client

How to use WebSocket on the front end?

Using WebSocket on the browser is very simple. You just need to create a WebSocket instance and listen to events:

 const socket = new WebSocket('ws://example.com/socket');

socket.addEventListener('open', function (event) {
    console.log('Connection established');
    socket.send('Hello Server!');
});

socket.addEventListener('message', function (event) {
    console.log('Received message:', event.data);
});

Common events include:

• open : Triggered after the connection is established
• message : fired when a server message is received
• error : Triggered when an error occurs
• close : Triggered when the connection is closed

You can add your own business logic to these event handling functions, such as updating page content, displaying notifications, etc.

How to support WebSocket in the backend?

Different backend languages have different implementation methods for WebSocket. Taking Node.js as an example, you can use the ws library to quickly build WebSocket services:

 const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });

wss.on('connection', function connection(ws) {
    ws.on('message', function incoming(message) {
        console.log('received:', message);
        ws.send(`server response: ${message}`);
    });
});

In this example, we create a WebSocket server that listens to port 8080. When there is a client connection, it listens for its message and sends a response back.

If you are using a framework like Express, you can also use ws and Express to let WebSocket and HTTP share a port.

What should I pay attention to when using WebSocket?

Although WebSocket is very powerful, there are some things to pay attention to in actual use:

• Handling of connection failure : Not all environments support WebSocket, such as some old proxy or firewalls that may block connections. It is recommended to downgrade, such as switching to long polling.
• Reconnection mechanism : Network instability may cause connection disconnection, and it is best to add automatic reconnection logic to the client.
• Security : Use wss:// (WebSocket Secure) to encrypt transmissions to avoid man-in-the-middle attacks.
• Message format specification : It is recommended to use JSON format to deliver messages in a unified manner to facilitate front-end and back-end parsing.

For example, adding a simple reconnect logic can be written like this:

 let socket;
function connect() {
    socket = new WebSocket('ws://example.com/socket');

    socket.addEventListener('close', () => {
        console.log('Connection is closed, reconnect after 5 seconds');
        setTimeout(connect, 5000);
    });
}
connect();

Basically that's it. Although WebSocket is not complicated, it is necessary to pay attention to connection management, exception handling and performance optimization to run stably.

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