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EventEmitter
Extended by process
The EventEmitter class is defined and exposed by the events module:
const EventEmitter = require('events');All EventEmitters emit the event 'newListener' when new listeners are added and 'removeListener' when existing listeners are removed.
Methods 15
Alias for EventEmitter.on
| Parameters | Type | Description |
|---|---|---|
| eventName | String | The event name |
| listener | Function | The event listener/callback function |
Synchronously calls each of the listeners registered for the event named eventName, in the order they were registered, passing the supplied arguments to each.
Returns true if the event had listeners, false otherwise.
| Parameters | Type | Description |
|---|---|---|
| eventName | String | The event name |
| args? | any | Optional arguments to pass along to event listeners |
Returns an array listing the events for which the emitter has registered listeners.
Returns the current max listener value for the EventEmitter which is either set by EventEmitter.setMaxListeners or defaults to events.defaultMaxListeners.
Returns the number of listeners listening to the event named eventName.
| Parameters | Type | Description |
|---|---|---|
| eventName | String | The event name |
Returns a copy of the array of listeners for the event named eventName.
| Parameters | Type | Description |
|---|---|---|
| eventName | String | The event name |
Alias for EventEmitter.removeListener.
| Parameters | Type | Description |
|---|---|---|
| eventName | String | The event name |
| listener | Function | The event listener/callback function |
Adds the listener function to the end of the listeners array for the event named eventName.
No checks are made to see if the listener has already been added.
Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.
| Parameters | Type | Description |
|---|---|---|
| eventName | String | The event name |
| listener | Function | The event listener/callback function |
Adds a one-time listener function for the event named eventName. The next time eventName is triggered, this listener is removed and then invoked.
| Parameters | Type | Description |
|---|---|---|
| eventName | String | The event name |
| listener | Function | The event listener/callback function |
Adds the listener function to the beginning of the listeners array for the event named eventName.
No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.
| Parameters | Type | Description |
|---|---|---|
| eventName | String | The event name |
| listener | Function | The event listener/callback function |
Adds a one-time listener function for the event named eventName to the beginning of the listeners array. The next time eventName is triggered, this listener is removed, and then invoked.
| Parameters | Type | Description |
|---|---|---|
| eventName | String | The event name |
| listener | Function | The event listener/callback function |
Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).
| Parameters | Type | Description |
|---|---|---|
| eventName | String | The event name |
Removes all listeners, or those of the specified eventName.
It is bad practice to remove listeners added elsewhere in the code, particularly when the EventEmitter instance was created by some other component or module (e.g. sockets or file streams).
Returns a reference to the EventEmitter, so that calls can be chained.
| Parameters | Type | Description |
|---|---|---|
| eventName? | String | The event name |
Removes the specified listener from the listener array for the event named eventName.
| Parameters | Type | Description |
|---|---|---|
| eventName | String | The event name |
| listener | Function | The event listener/callback function |
By default EventEmitters will print a warning if more than 10 listeners are added for a particular event.
This is a useful default that helps finding memory leaks.
The emitter.setMaxListeners() method allows the limit to be modified for this specific EventEmitter instance.
The value can be set to Infinity (or 0) to indicate an unlimited number of listeners.
| Parameters | Type | Description |
|---|---|---|
| n | Number | new max listener count |
Events 2
The 'newListener' event is emitted after the listener is added.
| Event properties | Type | Description |
|---|---|---|
| eventName | String | The event name |
| listener | Function | The event handler function |
The 'removeListener' event is emitted after the listener is removed.
| Event properties | Type | Description |
|---|---|---|
| eventName | String | The event name |
| listener | Function | The event handler function |