Difference between on() and add.listener() function in Node.js

In this article, we will discuss the difference between on() and add.listener() function in C++. Before discussing their differences, we must know about on() and addlistener() with their features.

What is the On() function?

It is done by adding a listener to an EventEmitter for a specified event in Node.js, using the on() method. In order to have a better view of the code and follow the rules of JavaScript in event handling, it is the recommended and more common way of registering listeners. Since on() is an alternate way inside this implementation for addListener(), there is no difference in use. But on() is chosen to be used because it fits in with modern JavaScript event handling, which makes it more understandable and natural for those already accustomed to event-driven programming.

Syntax:

It has the following syntax:

What is the Add.listerner()?

The addListener() method also registers an EventEmitter instance with a Node.js event listener, and the same happens to be active upon reception of the designated event. AddListener() is less common than using on() for this same purpose because on() is an alias for addListener(). In real life, on() is what you would use because it's readable and conventional. However, AddListener() is what works and what you will find in some older applications. The two approaches are functionally the same and equivalent when attaching event handlers to events on EventEmitter objects.

Syntax:

It has the following syntax:

Purpose:

AddListener() and on() are two methods available to add listeners (event handlers) to an EventEmitter instance for a specified event. The order in which listeners will be called is based on the order in which they were added when the event was emitted.

Example 1:

Output:

 Hello from on()! Hello from addListener()! 

Explanation:

• Both addListener() and on() methods attach the listener function to the 'greet' event.
• When emitter.emit('greet') is called, both of these listeners are going to run, in the order in which they were added.
• Since both methods respond to the event that is released, the result shows that they function similarly.

Example 2:

Output:

 --- Emitting "start" event --- Started event handled by on()! Started event handled by addListener()! --- Emitting "progress" event --- Progress event: Step 1 handled by on()! Progress event: Step 1 handled by addListener()! Progress event: Step 2 handled by on()! Progress event: Step 2 handled by addListener()! Progress event: Step 3 handled by on()! Progress event: Step 3 handled by addListener()! 

Explanation:

• In this example, use AddListener() and on() to add listeners for the "start" and "progress" events.
• The 'start' event is broadcast first, activating the listeners that were added using on() and addListener().
• Multiple Emissions: Three distinct emissions, each with a different step value, are produced from the "progress" event. Both methods respond to multiple event emissions with reliability, as demonstrated by the on() and addListener() listeners, which handle the event each time it is emitted.

Conclusion:

In conclusion, the on() and addListener() functions in Node.js are used to associate such event listeners with an EventEmitter such that the event-driven and therefore responsive application may execute. Since on() is synonymous with addListener() and serves the same purpose, it is the preferred choice and is used much more, due to its ease of reading the code and also because it is compliant with modern JavaScript standards. The fact of the matter is that both mechanisms can register listeners for one-time or recurring events, processing events in the order that listeners are registered, to support many listeners for a single event. Though addListener() function exists for backward compatibility, and On() finds itself used in new projects due to ease of use and adherence to modern JavaScript code standards.