Скачать или смотреть Understanding Why the socket.on() Function Gets Repeated in Node.js

Learn how to prevent the `socket.on()` function in Node.js from registering multiple times, causing unexpected behavior in your application.
---
This video is based on the question https://stackoverflow.com/q/63575854/ asked by the user 'stackmember' ( https://stackoverflow.com/u/14159415/ ) and on the answer https://stackoverflow.com/a/63575932/ provided by the user 'Rahul Bhobe' ( https://stackoverflow.com/u/11057988/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Why does the socket.on function gets repeated?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding Why the socket.on() Function Gets Repeated in Node.js

As a beginner diving into Node.js and Socket.IO, you may encounter unexpected behaviors in your code. One common issue arises when a callback function registered with socket.on() is executed multiple times, leading to redundant actions. This post will explain this problem and provide an easy fix to ensure your application runs smoothly.

The Problem: Repeated socket.on() Function Calls

You might face a situation where you notice the socket event listener for rannumber gets triggered multiple times. Here’s a typical scenario from a codebase:

You have an HTML button (in this case, a dice) that, when clicked, calls the happy() function.

Each time happy() is executed, a new listener for the rannumber event is registered.

Symptoms

When you click the dice, everything works fine the first time.

On subsequent clicks, you see that the socket.on('rannumber') function is called multiple times - the first time, it runs once, the second time it runs twice, and so forth.

Why Is This Happening?

The reason for such behavior is straightforward:

Every time you call the happy() function, a new callback is registered for socket.on('rannumber', ...).

This means that when the rannumber event emits a value, all callbacks that have been registered will be executed, leading to repeated outputs or actions which are not intended.

The Solution: Register the Callback Once

To resolve this issue, you'll want to ensure that the listener for the rannumber event is registered just once. Here’s how you can implement this fix effectively.

Step-by-Step Guide

Move the Listener Registration: Take the event listener registration out of the happy() function.

Set Up the Listener Once: Establish the socket.on('rannumber', ...) listener when your application starts, rather than each time the happy() function is called.

Here's how your code should look after applying these changes:

[[See Video to Reveal this Text or Code Snippet]]

Summary of Changes

Before: Listener was registered within the happy() function leading to multiple registrations.

After: Moved the listener outside, so it's registered only once during the initial socket connection setup.

Conclusion

By understanding why your socket.on() function was firing multiple times, you can easily rectify the issue by restructuring your code. This will ensure that your application behaves as expected, streamlining the communication between your client and server using Node.js and Socket.IO.

If you continue to experiment with Node.js, keep an eye out for similar patterns, as they can lead to baffling bugs. Happy coding!