Class: fs.StatWatcher
Class: fs.StatWatcher
(add-listener stat-watcher event-name listener)
Alias for emitter.on(eventName, listener)
.
Parameters:
event-name
: string | symbol
listener
: (...args: any[]) => void
Returns: StatWatcher
Alias for `emitter.on(eventName, listener)`. **Parameters:** - `event-name`: `string | symbol` - `listener`: `(...args: any[]) => void` **Returns:** `StatWatcher`
(emit? stat-watcher event-name & args)
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.
import { EventEmitter } from 'node:events';
const myEmitter = new EventEmitter();
// First listener
myEmitter.on('event', function firstListener() {
console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
const parameters = args.join(', ');
console.log(`event with parameters ${parameters} in third listener`);
});
console.log(myEmitter.listeners('event'));
myEmitter.emit('event', 1, 2, 3, 4, 5);
// Prints:
// [
// [Function: firstListener],
// [Function: secondListener],
// [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener
Parameters:
event-name
: string | symbol
args
: AnyRest
Returns: boolean
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. ```js import { EventEmitter } from 'node:events'; const myEmitter = new EventEmitter(); // First listener myEmitter.on('event', function firstListener() { console.log('Helloooo! first listener'); }); // Second listener myEmitter.on('event', function secondListener(arg1, arg2) { console.log(`event with parameters ${arg1}, ${arg2} in second listener`); }); // Third listener myEmitter.on('event', function thirdListener(...args) { const parameters = args.join(', '); console.log(`event with parameters ${parameters} in third listener`); }); console.log(myEmitter.listeners('event')); myEmitter.emit('event', 1, 2, 3, 4, 5); // Prints: // [ // [Function: firstListener], // [Function: secondListener], // [Function: thirdListener] // ] // Helloooo! first listener // event with parameters 1, 2 in second listener // event with parameters 1, 2, 3, 4, 5 in third listener ``` **Parameters:** - `event-name`: `string | symbol` - `args`: `AnyRest` **Returns:** `boolean`
(event-names stat-watcher)
Returns an array listing the events for which the emitter has registered
listeners. The values in the array are strings or Symbol
s.
import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});
const sym = Symbol('symbol');
myEE.on(sym, () => {});
console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]
Returns: (string | symbol)[]
Returns an array listing the events for which the emitter has registered listeners. The values in the array are strings or `Symbol`s. ```js import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => {}); myEE.on('bar', () => {}); const sym = Symbol('symbol'); myEE.on(sym, () => {}); console.log(myEE.eventNames()); // Prints: [ 'foo', 'bar', Symbol(symbol) ] ``` **Returns:** `(string | symbol)[]`
(listener-count stat-watcher event-name)
(listener-count stat-watcher event-name listener)
Returns the number of listeners listening for the event named eventName
.
If listener
is provided, it will return how many times the listener is found
in the list of the listeners of the event.
Parameters:
event-name
: string | symbol
- The name of the event being listened forlistener
: Function | undefined
- The event handler functionReturns: number
Returns the number of listeners listening for the event named `eventName`. If `listener` is provided, it will return how many times the listener is found in the list of the listeners of the event. **Parameters:** - `event-name`: `string | symbol` - The name of the event being listened for - `listener`: `Function | undefined` - The event handler function **Returns:** `number`
(listeners stat-watcher event-name)
Returns a copy of the array of listeners for the event named eventName
.
server.on('connection', (stream) => {
console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
Parameters:
event-name
: string | symbol
Returns: Function[]
Returns a copy of the array of listeners for the event named `eventName`. ```js server.on('connection', (stream) => { console.log('someone connected!'); }); console.log(util.inspect(server.listeners('connection'))); // Prints: [ [Function] ] ``` **Parameters:** - `event-name`: `string | symbol` **Returns:** `Function[]`
(max-listeners stat-watcher)
Returns the current max listener value for the EventEmitter
which is either
set by emitter.setMaxListeners(n)
or defaults to {@link defaultMaxListeners }.
Returns: number
Returns the current max listener value for the `EventEmitter` which is either set by `emitter.setMaxListeners(n)` or defaults to {@link defaultMaxListeners }. **Returns:** `number`
(off stat-watcher event-name listener)
Alias for emitter.removeListener()
.
Parameters:
event-name
: string | symbol
listener
: (...args: any[]) => void
Returns: StatWatcher
Alias for `emitter.removeListener()`. **Parameters:** - `event-name`: `string | symbol` - `listener`: `(...args: any[]) => void` **Returns:** `StatWatcher`
(on stat-watcher event-name listener)
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.
server.on('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the EventEmitter
, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The emitter.prependListener()
method can be used as an alternative to add the
event listener to the beginning of the listeners array.
import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.on('foo', () => console.log('a'));
myEE.prependListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
Parameters:
event-name
: string | symbol
- The name of the event.listener
: (...args: any[]) => void
- The callback functionReturns: StatWatcher
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. ```js server.on('connection', (stream) => { console.log('someone connected!'); }); ``` Returns a reference to the `EventEmitter`, so that calls can be chained. By default, event listeners are invoked in the order they are added. The `emitter.prependListener()` method can be used as an alternative to add the event listener to the beginning of the listeners array. ```js import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => console.log('a')); myEE.prependListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a ``` **Parameters:** - `event-name`: `string | symbol` - The name of the event. - `listener`: `(...args: any[]) => void` - The callback function **Returns:** `StatWatcher`
(once stat-watcher event-name listener)
Adds a one-time listener
function for the event named eventName
. The
next time eventName
is triggered, this listener is removed and then invoked.
server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the EventEmitter
, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The emitter.prependOnceListener()
method can be used as an alternative to add the
event listener to the beginning of the listeners array.
import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
Parameters:
event-name
: string | symbol
- The name of the event.listener
: (...args: any[]) => void
- The callback functionReturns: StatWatcher
Adds a **one-time** `listener` function for the event named `eventName`. The next time `eventName` is triggered, this listener is removed and then invoked. ```js server.once('connection', (stream) => { console.log('Ah, we have our first user!'); }); ``` Returns a reference to the `EventEmitter`, so that calls can be chained. By default, event listeners are invoked in the order they are added. The `emitter.prependOnceListener()` method can be used as an alternative to add the event listener to the beginning of the listeners array. ```js import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.once('foo', () => console.log('a')); myEE.prependOnceListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a ``` **Parameters:** - `event-name`: `string | symbol` - The name of the event. - `listener`: `(...args: any[]) => void` - The callback function **Returns:** `StatWatcher`
(prepend-listener stat-watcher event-name listener)
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.
server.prependListener('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the EventEmitter
, so that calls can be chained.
Parameters:
event-name
: string | symbol
- The name of the event.listener
: (...args: any[]) => void
- The callback functionReturns: StatWatcher
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. ```js server.prependListener('connection', (stream) => { console.log('someone connected!'); }); ``` Returns a reference to the `EventEmitter`, so that calls can be chained. **Parameters:** - `event-name`: `string | symbol` - The name of the event. - `listener`: `(...args: any[]) => void` - The callback function **Returns:** `StatWatcher`
(prepend-once-listener stat-watcher event-name listener)
Adds a one-timelistener
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.
server.prependOnceListener('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the EventEmitter
, so that calls can be chained.
Parameters:
event-name
: string | symbol
- The name of the event.listener
: (...args: any[]) => void
- The callback functionReturns: StatWatcher
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. ```js server.prependOnceListener('connection', (stream) => { console.log('Ah, we have our first user!'); }); ``` Returns a reference to the `EventEmitter`, so that calls can be chained. **Parameters:** - `event-name`: `string | symbol` - The name of the event. - `listener`: `(...args: any[]) => void` - The callback function **Returns:** `StatWatcher`
(raw-listeners stat-watcher event-name)
Returns a copy of the array of listeners for the event named eventName
,
including any wrappers (such as those created by .once()
).
import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));
// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];
// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();
// Logs "log once" to the console and removes the listener
logFnWrapper();
emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');
// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');
Parameters:
event-name
: string | symbol
Returns: Function[]
Returns a copy of the array of listeners for the event named `eventName`, including any wrappers (such as those created by `.once()`). ```js import { EventEmitter } from 'node:events'; const emitter = new EventEmitter(); emitter.once('log', () => console.log('log once')); // Returns a new Array with a function `onceWrapper` which has a property // `listener` which contains the original listener bound above const listeners = emitter.rawListeners('log'); const logFnWrapper = listeners[0]; // Logs "log once" to the console and does not unbind the `once` event logFnWrapper.listener(); // Logs "log once" to the console and removes the listener logFnWrapper(); emitter.on('log', () => console.log('log persistently')); // Will return a new Array with a single function bound by `.on()` above const newListeners = emitter.rawListeners('log'); // Logs "log persistently" twice newListeners[0](); emitter.emit('log'); ``` **Parameters:** - `event-name`: `string | symbol` **Returns:** `Function[]`
(ref stat-watcher)
When called, requests that the Node.js event loop not exit so long as the fs.StatWatcher
is active. Calling watcher.ref()
multiple times will have
no effect.
By default, all fs.StatWatcher
objects are "ref'ed", making it normally
unnecessary to call watcher.ref()
unless watcher.unref()
had been
called previously.
Returns: StatWatcher
When called, requests that the Node.js event loop _not_ exit so long as the `fs.StatWatcher` is active. Calling `watcher.ref()` multiple times will have no effect. By default, all `fs.StatWatcher` objects are "ref'ed", making it normally unnecessary to call `watcher.ref()` unless `watcher.unref()` had been called previously. **Returns:** `StatWatcher`
(remove-all-listeners stat-watcher)
(remove-all-listeners stat-watcher 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:
event-name
: string | symbol | undefined
Returns: StatWatcher
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:** - `event-name`: `string | symbol | undefined` **Returns:** `StatWatcher`
(remove-listener stat-watcher event-name listener)
Removes the specified listener
from the listener array for the event named eventName
.
const callback = (stream) => {
console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);
removeListener()
will remove, at most, one instance of a listener from the
listener array. If any single listener has been added multiple times to the
listener array for the specified eventName
, then removeListener()
must be
called multiple times to remove each instance.
Once an event is emitted, all listeners attached to it at the
time of emitting are called in order. This implies that any removeListener()
or removeAllListeners()
calls after emitting and before the last listener finishes execution
will not remove them fromemit()
in progress. Subsequent events behave as expected.
import { EventEmitter } from 'node:events';
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
const callbackA = () => {
console.log('A');
myEmitter.removeListener('event', callbackB);
};
const callbackB = () => {
console.log('B');
};
myEmitter.on('event', callbackA);
myEmitter.on('event', callbackB);
// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
// A
// B
// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
// A
Because listeners are managed using an internal array, calling this will
change the position indices of any listener registered after the listener
being removed. This will not impact the order in which listeners are called,
but it means that any copies of the listener array as returned by
the emitter.listeners()
method will need to be recreated.
When a single function has been added as a handler multiple times for a single
event (as in the example below), removeListener()
will remove the most
recently added instance. In the example the once('ping')
listener is removed:
import { EventEmitter } from 'node:events';
const ee = new EventEmitter();
function pong() {
console.log('pong');
}
ee.on('ping', pong);
ee.once('ping', pong);
ee.removeListener('ping', pong);
ee.emit('ping');
ee.emit('ping');
Returns a reference to the EventEmitter
, so that calls can be chained.
Parameters:
event-name
: string | symbol
listener
: (...args: any[]) => void
Returns: StatWatcher
Removes the specified `listener` from the listener array for the event named `eventName`. ```js const callback = (stream) => { console.log('someone connected!'); }; server.on('connection', callback); // ... server.removeListener('connection', callback); ``` `removeListener()` will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified `eventName`, then `removeListener()` must be called multiple times to remove each instance. Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that any `removeListener()` or `removeAllListeners()` calls _after_ emitting and _before_ the last listener finishes execution will not remove them from`emit()` in progress. Subsequent events behave as expected. ```js import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); const callbackA = () => { console.log('A'); myEmitter.removeListener('event', callbackB); }; const callbackB = () => { console.log('B'); }; myEmitter.on('event', callbackA); myEmitter.on('event', callbackB); // callbackA removes listener callbackB but it will still be called. // Internal listener array at time of emit [callbackA, callbackB] myEmitter.emit('event'); // Prints: // A // B // callbackB is now removed. // Internal listener array [callbackA] myEmitter.emit('event'); // Prints: // A ``` Because listeners are managed using an internal array, calling this will change the position indices of any listener registered _after_ the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the `emitter.listeners()` method will need to be recreated. When a single function has been added as a handler multiple times for a single event (as in the example below), `removeListener()` will remove the most recently added instance. In the example the `once('ping')` listener is removed: ```js import { EventEmitter } from 'node:events'; const ee = new EventEmitter(); function pong() { console.log('pong'); } ee.on('ping', pong); ee.once('ping', pong); ee.removeListener('ping', pong); ee.emit('ping'); ee.emit('ping'); ``` Returns a reference to the `EventEmitter`, so that calls can be chained. **Parameters:** - `event-name`: `string | symbol` - `listener`: `(...args: any[]) => void` **Returns:** `StatWatcher`
(set-max-listeners stat-watcher n)
By default EventEmitter
s 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.
Returns a reference to the EventEmitter
, so that calls can be chained.
Parameters:
n
: number
Returns: StatWatcher
By default `EventEmitter`s 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. Returns a reference to the `EventEmitter`, so that calls can be chained. **Parameters:** - `n`: `number` **Returns:** `StatWatcher`
(unref stat-watcher)
When called, the active fs.StatWatcher
object will not require the Node.js
event loop to remain active. If there is no other activity keeping the
event loop running, the process may exit before the fs.StatWatcher
object's
callback is invoked. Calling watcher.unref()
multiple times will have
no effect.
Returns: StatWatcher
When called, the active `fs.StatWatcher` object will not require the Node.js event loop to remain active. If there is no other activity keeping the event loop running, the process may exit before the `fs.StatWatcher` object's callback is invoked. Calling `watcher.unref()` multiple times will have no effect. **Returns:** `StatWatcher`
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