Communication

Introduction

Modern web applications rely heavily on fast, efficient, and interactive communication between the browser and the server. Whether you’re building chat apps, notification systems, live dashboards, or multiplayer tools, the way data moves behind the scenes determines how smooth the user experience will be. Two common approaches that developers use to update content without refreshing the entire web page are Ajax and Comet. Although both aim to improve real-time interaction, they accomplish this in different ways and are suited for different tasks.

This article explains the key differences between Comet and Ajax, how they work, when to choose one over the other, and why they remain important even with today’s modern technologies.

What Is Ajax?

Definition

Ajax (Asynchronous JavaScript and XML) is a web development technique that allows a webpage to communicate with a server in the background. This means the page can update portions of content without requiring a full reload.

How Ajax Works

Ajax uses:

• JavaScript

• HTTP requests

• The browser’s XMLHttpRequest (XHR) object or Fetch API

A typical Ajax process looks like this:

1. The browser sends a request to the server.

2. The server processes the request.

3. The server responds with data.

4. Only part of the webpage updates using JavaScript.

This gives users a faster, smoother experience because the whole page does not refresh.

Common Uses of Ajax

Ajax is ideal for:

• Form validation

• Search suggestions

• Loading data dynamically

• Updating small parts of a webpage

• Submitting forms without reload

Ajax became a key technology that powered early interactive sites like social platforms, dashboards, and messaging services before full real-time tech was widely available.

What Is Comet?

Definition

Comet is a web communication technique that allows the server to push data to the browser without the browser constantly refreshing or sending repeated requests.

Comet is sometimes called:

• Server push

• Reverse Ajax

• Long-polling mechanism

Comet creates a more “real-time” environment compared to traditional Ajax.

How Comet Works

Comet typically works in two major ways:

1. Long Polling

• The browser sends a request.

• The server holds the request open until new data is ready.

• When new data becomes available, the server responds.

• The browser immediately sends a new long-poll request.

This creates a continuous connection feeling even though each request eventually closes.

2. Streaming

• The browser opens a connection to the server.

• The server continuously sends updates through the same connection.

• The connection remains open for a long time, delivering near real-time data.

Streaming is more efficient than long polling but depends on browser and server support.

Common Uses of Comet

Comet works best for:

• Live chat applications

• Real-time notifications

• Live sports scores

• Stock market updates

• Multiplayer games

• Any app requiring instant updates

While Comet has been partly replaced by WebSockets, many systems still use it because it works on older browsers and is easy to integrate.

Key Differences Between Comet and Ajax

1. Direction of Communication

Ajax

• The browser initiates every request.

• The server only responds when asked.

Comet

• The server can send data as soon as it becomes available.

• Communication feels more bidirectional.

Winner (for real-time apps): Comet

2. Real-Time Capability

Ajax

• Not true real-time.

• Requires the client to repeatedly check for updates (polling).

• Slow or inefficient for fast-changing data.

Comet

• Provides near real-time updates.

• Server pushes data immediately when events occur.

Winner: Comet

3. Server Load

Ajax

• Frequent polling can overload the server with unnecessary requests.

• Good for occasional updates, bad for constant checks.

Comet

• Long-polling reduces the number of useless requests.

• More efficient for high-frequency updates.

Winner: Comet (for heavy traffic)

4. Complexity

Ajax

• Easy to implement.

• Supported by all browsers.

• Works well with simple APIs.

Comet

• More complex to build.

• Requires careful server handling.

• Harder to debug and manage connections.

Winner: Ajax (for simplicity)

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5. Use Cases

Ajax

Best when:

• You need occasional updates

• Your data does not change rapidly

• You want quick and simple implementation

Comet

Best when:

• You need instant updates

• The user interface must stay synchronized

• Real-time events matter

Examples:

• Ajax → product searches, weather data loading

• Comet → chat messaging, real-time sports scores

Comet vs Ajax: Performance Comparison

Speed

• Comet provides faster updates because you don’t wait for a polling cycle.

• Ajax may introduce delays depending on the polling interval.

Network Usage

• Ajax uses more bandwidth due to repeated requests.

• Comet uses fewer requests but keeps connections open longer.

Scalability

• Comet requires more server resources to maintain open connections.

• Ajax can scale easily but becomes inefficient at high update rates.

Browser Support

• Ajax works everywhere.

• Comet works in modern browsers but may behave differently across older ones.

Advantages of Ajax

• Easy to implement

• Great for partial updates

• Reduces full page reloads

• Works with Fetch API and frameworks

• Reliable and well-understood technology

Ajax remains a foundation of modern front-end development Advantages of Comet

• Real-time feel without WebSockets

• Reduces unnecessary requests

• Ideal for fast-changing data

• Creates interactive, live experiences

Comet is a bridge between older web methods and modern real-time systems.

Disadvantages of Ajax

• Not truly real-time

• High server load during polling

• Delay between updates

• Inefficient for rapid events

Disadvantages of Comet

• More complex to write

• Harder to scale for thousands of users

• Requires advanced server configuration

• Persistent connections may strain older systems

Comet vs Ajax: Which One Should You Choose?

Choose Ajax if:

• Your app only needs occasional updates

• You want simple and reliable implementation

• You are updating small parts of the UI

• You do not require instant communication

Examples:

• News loading

• Form suggestions

• Dashboard refresh every few minutes

Choose Comet if:

• Your app needs real-time data

• Updates must appear instantly

• You have event-driven applications

• You want a push-style data flow

Examples:

• Chat platforms

• Real-time notifications

• Live messages

• Multiplayer interactions

Conclusion

Comet and Ajax both play important roles in modern web communication. Ajax allows efficient background requests and partial page updates, making it perfect for traditional interactive websites. Comet, however, brings the web closer to real-time communication by enabling the server to push data to the client as soon as it’s ready.

Choosing between Comet and Ajax depends entirely on your application’s needs. If your project involves live data and instant updates, Comet is the stronger choice. If you simply need to update parts of a webpage without reloading, Ajax is simpler, lighter, and more efficient.

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