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The Node events module

The Node events module

The events module of Node.js provides the EventEmitter class.

The events module provides us with the EventEmitter class, which is essential for working with events in Node. I have written a detailed article on this topic, which you can find here. In this blog, I will describe the API without providing further examples on how to use it.

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const EventEmitter = require('events')
const door = new EventEmitter()

The EventEmitter class uses the following events internally:

  • newListener: triggered when a listener is added.
  • removeListener: triggered when a listener is removed.

Here is a detailed description of the most useful methods:

  • emitter.addListener() (alias for emitter.on()): Adds a listener to an event.
  • emitter.emit(): Emits an event and calls every event listener in the order they were registered.
  • emitter.eventNames(): Returns an array of strings representing the registered events on the current EventEmitter instance.
  • emitter.getMaxListeners(): Gets the maximum number of listeners that can be added to an EventEmitter object. The default value is 10 but can be increased or decreased using setMaxListeners().
  • emitter.listenerCount(): Gets the count of listeners for a specific event.
  • emitter.listeners(): Returns an array of listeners for a specific event.
  • emitter.off() (alias for emitter.removeListener()): Removes a specific listener from the EventEmitter.
  • emitter.on(): Adds a callback function to be called when an event is emitted.
  • emitter.once(): Adds a callback function to be called only for the first occurrence of an event.
  • emitter.prependListener(): Adds a listener to the beginning of the listeners queue for an event.
  • emitter.prependOnceListener(): Adds a listener to be called before other listeners when an event is emitted for the first time.
  • emitter.removeAllListeners(): Removes all listeners for a specific event from the EventEmitter object.
  • emitter.removeListener(): Removes a specific listener from the EventEmitter object. The callback function can be referenced using a variable.
  • emitter.setMaxListeners(): Sets the maximum number of listeners that can be added to an EventEmitter object.

Tags: Node.js, events module, EventEmitter