Exploring EventEmitter class

EventEmitter class implements pub-sub design pattern, it is defined in events module.

Below table summarizes the events provided by EventEmitter class.

Event	Description
newListener	This event is emitted before a listener is added to its internal array of listeners.
removeListener	This event is emitted after the listener is removed.

Below table summarizes the methods provided by EventEmitter class.

S.No	Method and Description
1	emitter.addListener(eventName, listener) This function add listener to this event.
2	emitter.emit(eventName[, ...args]) This function calls all the listeners registered for this event synchronously.
3	emitter.eventNames() Returns an array listing the events for which the emitter has registered listeners.
4	emitter.getMaxListeners() Returns the current max listener value for the EventEmitter. You can set the maximum listeners for an event to the emitter by calling ‘setMaxListeners(n)’. If you do not set maximum listeners value explicitly, then the ‘EventEmitter.defaultMaxListeners’ value is used as default value.
5	emitter.listenerCount(eventName) Returns a copy of the array of listeners for the event named eventName.
6	emitter.off(eventName, listener) It is an alias for emitter.removeListener(). It removes the specified listener from the listener array for the event named eventName.
7	emitter.on(eventName, listener) It adds a listener to this event.
8	emitter.once(eventName, listener) This method adds one-time listener to this event. Even though the event emitted more than one time, this listener called only once.
9	emitter.prependListener(eventName, listener) Prepend a listener function to the beginning of the array for the event named eventName.
10	emitter.prependOnceListener(eventName, listener) Prepend a one-time listener function for the event named eventName to the beginning of the listeners array.
11	emitter.removeAllListeners([eventName]) Remove all listeners associated with this event.
12	emitter.removeListener(eventName, listener) Removes the specified listener from the listener array for the event named eventName.
13	emitter.setMaxListeners(n) By default, EventEmitter allows 10 macimum listeners to an event. You can change this behavior using 'emitter.setMaxListeners(n)' method. The value ‘n’ can be set to Infinity (or 0) to indicate an unlimited number of listeners.
14	emitter.rawListeners(eventName) This method returns a copy of the array of listeners for the event named eventName.

‘EventEmitter.defaultMaxListeners’ specifies the default maximum listeners for an emitter instance for any single event. As per the node.js documentation, maximum default listeners are 10.

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