Difference between Polling and WebSockets

Polling and WebSockets are two different techniques for client-server communication, particularly useful for real-time applications. Here's a detailed comparison between the two, along with their use cases and examples:

Polling

Polling is a method where the client repeatedly requests data from the server at regular intervals.

How It Works:

• The client sends an HTTP request to the server at set intervals.
• The server processes the request and sends back the latest data.
• This process continues indefinitely or until stopped.

Types of Polling:

1. Regular Polling:

   • The client sends requests at fixed intervals regardless of whether new data is available.
   • Example: Sending a request every 5 seconds.

2. Long Polling:

   • The client sends a request and the server holds the connection open until new data is available or a timeout occurs.
   • Once the server responds, the client immediately sends another request, creating a near-real-time connection.

Advantages:

• Simple to implement.
• Works with any HTTP/HTTPS server.
• No special protocols or libraries are required.

Disadvantages:

• Inefficient use of resources due to frequent requests.
• Increased latency since data is updated only at polling intervals.
• Higher server load due to handling many repeated requests.

Example (Regular Polling in JavaScript):

function poll() {
    setInterval(async () => {
        const response = await fetch('/api/data');
        const data = await response.json();
        console.log(data);
    }, 5000); // Poll every 5 seconds
}

poll();

WebSockets

WebSockets provide a full-duplex communication channel over a single, long-lived connection between the client and the server.

How It Works:

• The client initiates a WebSocket connection by sending an HTTP request with an Upgrade header.
• The server upgrades the connection to a WebSocket if it supports the protocol.
• Once established, both the client and server can send and receive messages asynchronously.

Advantages:

• Low latency communication as data can be pushed to the client instantly.
• Efficient use of resources with a persistent connection.
• Reduces the need for repeated HTTP requests.

Disadvantages:

• More complex to implement and manage.
• Not all environments support WebSockets (e.g., some corporate networks block WebSocket connections).
• Requires WebSocket-compatible server infrastructure.

Example (WebSockets in JavaScript):

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

socket.onopen = function(event) {
    console.log('WebSocket connection opened.');
    socket.send('Hello Server!');
};

socket.onmessage = function(event) {
    console.log('Message from server:', event.data);
};

socket.onclose = function(event) {
    console.log('WebSocket connection closed.');
};

socket.onerror = function(event) {
    console.error('WebSocket error:', event);
};

Comparison Table

Feature	Polling	WebSockets
Communication	Client initiates each request	Full-duplex, bidirectional
Latency	Higher latency	Low latency
Efficiency	Less efficient (frequent requests)	More efficient (persistent connection)
Implementation	Simple	Complex
Compatibility	Works with any HTTP server	Requires WebSocket-compatible server
Use Case	Suitable for less frequent updates or simpler applications	Ideal for real-time applications (chat, live updates)

Use Cases

Polling:

• Applications where data changes infrequently and real-time updates are not critical.
• Scenarios where server load and efficiency are not primary concerns.

WebSockets:

• Real-time chat applications.
• Live sports scores and stock ticker updates.
• Online gaming and collaborative tools.