listener-tracker

Lightweight module to support tracking added event listeners for easy removal later.

Installation

npm install listener-tracker --save

Overview

The native Node.js events module makes it difficult to remove listeners since you must keep a reference to the listener function in order to remove it later. For example, to properly remove a listener you must do the following:

function fooListener() {
    /* ... */
}
 
// Add a listener:
eventEmitter.on('foo', fooListener);
 
// Now remove it:
eventEmitter.removeListener('foo', fooListener);

This is a problem because often times it is more convenient to add listeners with an anonymous function. For example:

// Add a listener:
eventEmitter.on('foo', function fooListener() {
    /* ... */
});
 
// How can we remove it???

Also, what if an object is being destroyed and needs to remove all listeners that were added to other EventEmitter instances? This module solves these types of problems by keeping tracking of all listeners that are attached by proxying all of the methods that are used to add listeners (i.e. on, once and addListener).

To prevent a memory leak resulting from keeping references to all of the listener functions that were attached, this module will automatically do cleanup if a target EventEmitter emits a destroy event. You can also manually remove all listeners, of course.

Usage

Tracking listeners for a single EventEmitter instance for easy removal

var EventEmitter = require('events').EventEmitter;
 
var myEventEmitter = EventEmitter();
var wrapped = require('listener-tracker').wrap(myEventEmitter);
 
wrapped
    .on('foo', function() { /* ... */ })
    .on('bar', function() { /* ... */ });
 
// Remove all of the listenters that were tracked by this instance:
wrapped.removeAllListeners();
 
// Remove the listenters that were tracked by this instance for a specific event:
wrapped.removeAllListeners('foo');

Tracking listeners to multiple EventEmitter instances for easy removal

var EventEmitter = require('events').EventEmitter;
 
var listenerTracker = require('listener-tracker').createTracker();
var eventEmitter1 = EventEmitter();
var eventEmitter2 = EventEmitter();
 
listenerTracker.subscribeTo(eventEmitter1)
    .on('foo', function() { /* ... */ })
    .on('bar', function() { /* ... */ });
 
listenerTracker.subscribeTo(eventEmitter2)
    .on('foo', function() { /* ... */ })
    .on('bar', function() { /* ... */ });
 
// Remove all listeners across all EventEmitters that were subscribed to:
listenerTracker.removeAllListeners();
 
// It's also possible to remove just listeners from one of the event emitters:
listenerTracker.removeAllListeners(eventEmitter1);
 
// Finally, it's also possible to remove just listeners from one of the event
// emitters for a specific event type:
listenerTracker.removeAllListeners(eventEmitter1, 'foo');

Contributors

• Patrick Steele-Idem (Twitter: @psteeleidem)
• Phillip Gates-Idem (Twitter: @philidem)

Contribute

Pull Requests welcome. Please submit Github issues for any feature enhancements, bugs or documentation problems.

License

Apache License v2.0