Optionalinfo: {StaticcaptureValue: boolean
Change the default captureRejections option on all new EventEmitter objects.
Static ReadonlycaptureValue: Symbol.for('nodejs.rejection')
See how to write a custom rejection handler.
StaticdefaultBy default, a maximum of 10 listeners can be registered for any single
event. This limit can be changed for individual EventEmitter instances
using the emitter.setMaxListeners(n) method. To change the default
for allEventEmitter instances, the events.defaultMaxListeners property
can be used. If this value is not a positive number, a RangeError is thrown.
Take caution when setting the events.defaultMaxListeners because the
change affects all EventEmitter instances, including those created before
the change is made. However, calling emitter.setMaxListeners(n) still has
precedence over events.defaultMaxListeners.
This is not a hard limit. The EventEmitter instance will allow
more listeners to be added but will output a trace warning to stderr indicating
that a "possible EventEmitter memory leak" has been detected. For any single
EventEmitter, the emitter.getMaxListeners() and emitter.setMaxListeners() methods can be used to
temporarily avoid this warning:
import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.setMaxListeners(emitter.getMaxListeners() + 1);
emitter.once('event', () => {
// do stuff
emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0));
});
The --trace-warnings command-line flag can be used to display the
stack trace for such warnings.
The emitted warning can be inspected with process.on('warning') and will
have the additional emitter, type, and count properties, referring to
the event emitter instance, the event's name and the number of attached
listeners, respectively.
Its name property is set to 'MaxListenersExceededWarning'.
Static ReadonlyerrorThis symbol shall be used to install a listener for only monitoring 'error' events. Listeners installed using this symbol are called before the regular 'error' listeners are called.
Installing a listener using this symbol does not change the behavior once an 'error' event is emitted. Therefore, the process will still crash if no
regular 'error' listener is installed.
Supported baud rates.
Name or description of the file creator (max 245 characters).
File creation time.
Constructs and returns the Eds DataObjects keyed by decimal string. This is provided to support old tools. For new code use the new Eds iterator methods (keyed by hex string) instead.
Use Eds#entries instead.
File description.
File name.
File revision (8-bit unsigned integer).
File version (8-bit unsigned integer).
Provides the granularity allowed for the mapping on this device - most devices support a granularity of 8. (8-bit integer, max 64).
Indicates if LSS functionality is supported.
Time of the last modification.
Name or description of the last modifier (max 244 characters).
The number of supported receive PDOs (16-bit unsigned integer).
The number of supported transmit PDOs (16-bit unsigned integer).
Product order code (max 245 characters).
Product name (max 243 characters).
Product code (32-bit unsigned integer).
Revision number (32-bit unsigned integer).
Indicates simple boot-up master functionality (not supported).
Indicates simple boot-up slave functionality (not supported).
Vendor name (max 244 characters).
Unique vendor ID (32-bit unsigned integer).
Optional[captureAdd an entry to object 0x1028 - Emergency consumer object.
COB-ID to add.
Optionaloptions: {DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalparameterName?: stringDataObject name.
OptionalsaveDefault?: booleansave value as default.
OptionalsubIndex?: numberindex to store the entry.
Create a new entry.
index of the data object.
data passed to the DataObject constructor.
Add an entry to object 0x1016 - Consumer heartbeat time.
device identifier [1-127].
milliseconds before a timeout is reported.
Optionaloptions: { accessType?: string; saveDefault?: boolean; subIndex?: number }DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalsaveDefault?: booleansave value as default.
OptionalsubIndex?: numberindex to store the entry.
Create a RPDO communication/mapping parameter object.
Object 0x1400..0x15FF - RPDO communication parameter
Sub-index 1 (mandatory):
Sub-index 2 (mandatory):
Sub-index 3 (optional):
Object 0x1600..0x17FF - RPDO mapping parameter
Inhibit time and synchronous RPDOs are not yet supported. All entries are treated as event-driven with an inhibit time of 0.
PDO data.
COB-ID used by the RPDO.
objects to map.
OptionalinhibitTime?: numberminimum time between updates.
OptionaltransmissionType?: numbertransmission type.
Optionaloptions: {optional arguments.
OptionalaccessType?: stringDataObject access type.
Optionalindex?: numberDataObject index [0x1400-0x15ff].
OptionalparameterName?: string[]DataObject names.
OptionalsaveDefault?: booleansave value as default.
Add an SDO client parameter object.
Object 0x1280..0x12FF - SDO client parameter.
Sub-index 1/2:
Sub-index 3:
device identifier [1-127].
OptionalcobIdTx: numberCOB-ID for outgoing messages (to server).
OptionalcobIdRx: numberCOB-ID for incoming messages (from server).
Optionaloptions: {DataObject creation options.
OptionalaccessType?: stringDataObject access type.
Optionalindex?: stringDataObject index [0x1200-0x127F].
OptionalparameterName?: stringDataObject name.
OptionalsaveDefault?: booleansave value as default.
Add an SDO server parameter object.
Object 0x1200..0x127F - SDO server parameter.
Sub-index 1/2:
Sub-index 3 (optional):
device identifier [1-127].
OptionalcobIdTx: numberCOB-ID for outgoing messages (to client).
OptionalcobIdRx: numberCOB-ID for incoming messages (from client).
Optionaloptions: {DataObject creation options.
OptionalaccessType?: stringDataObject access type.
Optionalindex?: stringDataObject index [0x1200-0x127F].
OptionalparameterName?: stringDataObject name.
OptionalsaveDefault?: booleansave value as default.
Create a new sub-entry.
index of the data object.
subIndex of the data object.
data passed to the DataObject constructor.
Create a TPDO communication/mapping parameter object.
Object 0x1800..0x19FF - TPDO communication parameter
Sub-index 1 (mandatory):
Sub-index 2 (mandatory):
Sub-index 3 (optional):
Sub-index 5 (optional):
Sub-index 6 (optional):
Object 0x2000..0x21FF - TPDO mapping parameter
object data.
COB-ID used by the TPDO.
objects to map.
OptionaleventTime?: numberhow often to send timer based PDOs.
OptionalinhibitTime?: numberminimum time between writes.
OptionalsyncStart?: numberinitial counter value for sync PDOs.
OptionaltransmissionType?: numbertransmission type.
Optionaloptions: { accessType?: string; index?: number; parameterName?: string[] }optional arguments.
OptionalaccessType?: stringDataObject access type.
Optionalindex?: numberDataObject index [0x1800-0x19ff].
OptionalparameterName?: string[]DataObject names.
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
Returns a new iterator object that iterates key/DataObjects pairs.
Iterable [key, DataObject].
Returns an array listing the events for which the emitter has registered
listeners. The values in the array are strings or Symbols.
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) ]
Get a data object by name.
name of the data object.
Get a data object by index.
index of the data object.
Returns the current max listener value for the EventEmitter which is either
set by emitter.setMaxListeners(n) or defaults to EventEmitter.defaultMaxListeners.
Get RPDO communication/mapping parameters.
mapped RPDOs.
Get a sub-entry.
index or name of the data object.
subIndex of the data object.
Get TPDO communication/mapping parameters.
mapped TPDOs.
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.
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] ]
Read and parse an EDS file.
path to file.
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
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
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.
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.
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');
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.
OptionaleventName: unknownDelete an entry.
index of the data object.
the deleted entry.
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.
Remove an RPDO communication/mapping parameter object.
COB-ID used by the RPDO.
removed RPDO.
Delete a sub-entry.
index of the data object.
subIndex of the data object.
Remove a TPDO communication/mapping parameter object.
COB-ID used by the TPDO.
removed TPDO.
Write an EDS file.
path to file, defaults to fileName.
Optionaloptions: { modificationDate?: Date; modifiedBy?: string }optional inputs.
OptionalmodificationDate?: Datefile modification date to file.
OptionalmodifiedBy?: stringfile modification date to file.
Set object 0x1015 - Inhibit time EMCY.
inhibit time in multiples of 100 μs.
Optionaloptions: { accessType?: string; saveDefault?: boolean }DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalsaveDefault?: booleansave value as default.
Set object 0x1001 - Error register.
error flags.
Optionalcommunication?: booleancommunication error.
Optionalcurrent?: booleancurrent error.
Optionaldevice?: booleandevice profile specific error.
Optionalgeneric?: booleangeneric error.
Optionalmanufacturer?: booleanmanufacturer specific error.
Optionaltemperature?: booleantemperature error.
Optionalvoltage?: booleanvoltage error.
Set object 0x1017 - Producer heartbeat time.
A value of zero disables the heartbeat.
Producer heartbeat time in ms.
Optionaloptions: { accessType?: string; saveDefault?: boolean }DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalsaveDefault?: booleansave value as default.
Set object 0x1018 - Identity object.
device identity.
product code.
revision number.
serial number.
vendor id.
Optionaloptions: { accessType?: string; saveDefault?: boolean }DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalsaveDefault?: booleansave value as default.
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.
Returns a reference to the EventEmitter, so that calls can be chained.
Set object 0x1005 - COB-ID SYNC.
Sync COB-ID (typically 0x80).
Optionaloptions: { accessType?: string; saveDefault?: boolean }DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalsaveDefault?: booleansave value as default.
Set object 0x1006 - Communication cycle period.
communication cycle period.
Optionaloptions: { accessType?: string; saveDefault?: boolean }DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalsaveDefault?: booleansave value as default.
Set object 0x1005 [bit 30] - Sync generation enable.
Sync generation enable.
Optionaloptions: { accessType?: string; saveDefault?: boolean }DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalsaveDefault?: booleansave value as default.
Set object 0x1019 - Synchronous counter overflow value.
Sync overflow value.
Optionaloptions: { accessType?: string; saveDefault?: boolean }DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalsaveDefault?: booleansave value as default.
Set object 0x1012 - COB-ID TIME.
Time COB-ID (typically 0x100).
Optionaloptions: { accessType?: string; saveDefault?: boolean }DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalsaveDefault?: booleansave value as default.
Set object 0x1012 [bit 31] - Time consumer enable.
Time consumer enable.
Optionaloptions: { accessType?: string; saveDefault?: boolean }DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalsaveDefault?: booleansave value as default.
Set object 0x1012 [bit 30] - Time producer enable.
Time producer enable.
Optionaloptions: { accessType?: string; saveDefault?: boolean }DataObject creation options.
OptionalaccessType?: stringDataObject access type.
OptionalsaveDefault?: booleansave value as default.
Returns a new iterator object that iterates DataObjects.
Iterable DataObjects.
StaticaddListens once to the abort event on the provided signal.
Listening to the abort event on abort signals is unsafe and may
lead to resource leaks since another third party with the signal can
call e.stopImmediatePropagation(). Unfortunately Node.js cannot change
this since it would violate the web standard. Additionally, the original
API makes it easy to forget to remove listeners.
This API allows safely using AbortSignals in Node.js APIs by solving these
two issues by listening to the event such that stopImmediatePropagation does
not prevent the listener from running.
Returns a disposable so that it may be unsubscribed from more easily.
import { addAbortListener } from 'node:events';
function example(signal) {
let disposable;
try {
signal.addEventListener('abort', (e) => e.stopImmediatePropagation());
disposable = addAbortListener(signal, (e) => {
// Do something when signal is aborted.
});
} finally {
disposable?.[Symbol.dispose]();
}
}
Disposable that removes the abort listener.
StaticfromStaticgetReturns a copy of the array of listeners for the event named eventName.
For EventEmitters this behaves exactly the same as calling .listeners on
the emitter.
For EventTargets this is the only way to get the event listeners for the
event target. This is useful for debugging and diagnostic purposes.
import { getEventListeners, EventEmitter } from 'node:events';
{
const ee = new EventEmitter();
const listener = () => console.log('Events are fun');
ee.on('foo', listener);
console.log(getEventListeners(ee, 'foo')); // [ [Function: listener] ]
}
{
const et = new EventTarget();
const listener = () => console.log('Events are fun');
et.addEventListener('foo', listener);
console.log(getEventListeners(et, 'foo')); // [ [Function: listener] ]
}
StaticgetReturns the currently set max amount of listeners.
For EventEmitters this behaves exactly the same as calling .getMaxListeners on
the emitter.
For EventTargets this is the only way to get the max event listeners for the
event target. If the number of event handlers on a single EventTarget exceeds
the max set, the EventTarget will print a warning.
import { getMaxListeners, setMaxListeners, EventEmitter } from 'node:events';
{
const ee = new EventEmitter();
console.log(getMaxListeners(ee)); // 10
setMaxListeners(11, ee);
console.log(getMaxListeners(ee)); // 11
}
{
const et = new EventTarget();
console.log(getMaxListeners(et)); // 10
setMaxListeners(11, et);
console.log(getMaxListeners(et)); // 11
}
StaticisStaticlistenerA class method that returns the number of listeners for the given eventName registered on the given emitter.
import { EventEmitter, listenerCount } from 'node:events';
const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2
The emitter to query
The event name
Staticonimport { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo')) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
Returns an AsyncIterator that iterates eventName events. It will throw
if the EventEmitter emits 'error'. It removes all listeners when
exiting the loop. The value returned by each iteration is an array
composed of the emitted event arguments.
An AbortSignal can be used to cancel waiting on events:
import { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ac = new AbortController();
(async () => {
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo', { signal: ac.signal })) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
})();
process.nextTick(() => ac.abort());
Use the close option to specify an array of event names that will end the iteration:
import { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
ee.emit('close');
});
for await (const event of on(ee, 'foo', { close: ['close'] })) {
console.log(event); // prints ['bar'] [42]
}
// the loop will exit after 'close' is emitted
console.log('done'); // prints 'done'
Optionaloptions: StaticEventEmitterIteratorOptionsAn AsyncIterator that iterates eventName events emitted by the emitter
import { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo')) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
Returns an AsyncIterator that iterates eventName events. It will throw
if the EventEmitter emits 'error'. It removes all listeners when
exiting the loop. The value returned by each iteration is an array
composed of the emitted event arguments.
An AbortSignal can be used to cancel waiting on events:
import { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ac = new AbortController();
(async () => {
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});
for await (const event of on(ee, 'foo', { signal: ac.signal })) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
})();
process.nextTick(() => ac.abort());
Use the close option to specify an array of event names that will end the iteration:
import { on, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
ee.emit('close');
});
for await (const event of on(ee, 'foo', { close: ['close'] })) {
console.log(event); // prints ['bar'] [42]
}
// the loop will exit after 'close' is emitted
console.log('done'); // prints 'done'
Optionaloptions: StaticEventEmitterIteratorOptionsAn AsyncIterator that iterates eventName events emitted by the emitter
StaticonceCreates a Promise that is fulfilled when the EventEmitter emits the given
event or that is rejected if the EventEmitter emits 'error' while waiting.
The Promise will resolve with an array of all the arguments emitted to the
given event.
This method is intentionally generic and works with the web platform EventTarget interface, which has no special'error' event
semantics and does not listen to the 'error' event.
import { once, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
process.nextTick(() => {
ee.emit('myevent', 42);
});
const [value] = await once(ee, 'myevent');
console.log(value);
const err = new Error('kaboom');
process.nextTick(() => {
ee.emit('error', err);
});
try {
await once(ee, 'myevent');
} catch (err) {
console.error('error happened', err);
}
The special handling of the 'error' event is only used when events.once() is used to wait for another event. If events.once() is used to wait for the
'error' event itself, then it is treated as any other kind of event without
special handling:
import { EventEmitter, once } from 'node:events';
const ee = new EventEmitter();
once(ee, 'error')
.then(([err]) => console.log('ok', err.message))
.catch((err) => console.error('error', err.message));
ee.emit('error', new Error('boom'));
// Prints: ok boom
An AbortSignal can be used to cancel waiting for the event:
import { EventEmitter, once } from 'node:events';
const ee = new EventEmitter();
const ac = new AbortController();
async function foo(emitter, event, signal) {
try {
await once(emitter, event, { signal });
console.log('event emitted!');
} catch (error) {
if (error.name === 'AbortError') {
console.error('Waiting for the event was canceled!');
} else {
console.error('There was an error', error.message);
}
}
}
foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!
Optionaloptions: StaticEventEmitterOptionsCreates a Promise that is fulfilled when the EventEmitter emits the given
event or that is rejected if the EventEmitter emits 'error' while waiting.
The Promise will resolve with an array of all the arguments emitted to the
given event.
This method is intentionally generic and works with the web platform EventTarget interface, which has no special'error' event
semantics and does not listen to the 'error' event.
import { once, EventEmitter } from 'node:events';
import process from 'node:process';
const ee = new EventEmitter();
process.nextTick(() => {
ee.emit('myevent', 42);
});
const [value] = await once(ee, 'myevent');
console.log(value);
const err = new Error('kaboom');
process.nextTick(() => {
ee.emit('error', err);
});
try {
await once(ee, 'myevent');
} catch (err) {
console.error('error happened', err);
}
The special handling of the 'error' event is only used when events.once() is used to wait for another event. If events.once() is used to wait for the
'error' event itself, then it is treated as any other kind of event without
special handling:
import { EventEmitter, once } from 'node:events';
const ee = new EventEmitter();
once(ee, 'error')
.then(([err]) => console.log('ok', err.message))
.catch((err) => console.error('error', err.message));
ee.emit('error', new Error('boom'));
// Prints: ok boom
An AbortSignal can be used to cancel waiting for the event:
import { EventEmitter, once } from 'node:events';
const ee = new EventEmitter();
const ac = new AbortController();
async function foo(emitter, event, signal) {
try {
await once(emitter, event, { signal });
console.log('event emitted!');
} catch (error) {
if (error.name === 'AbortError') {
console.error('Waiting for the event was canceled!');
} else {
console.error('There was an error', error.message);
}
}
}
foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!
Optionaloptions: StaticEventEmitterOptionsStaticsetimport { setMaxListeners, EventEmitter } from 'node:events';
const target = new EventTarget();
const emitter = new EventEmitter();
setMaxListeners(5, target, emitter);
Optionaln: numberA non-negative number. The maximum number of listeners per EventTarget event.
Zero or more {EventTarget} or {EventEmitter} instances. If none are specified, n is set as the default max for all newly created {EventTarget} and {EventEmitter}
objects.
A CANopen Electronic Data Sheet.
This class provides methods for loading and saving CANopen EDS v4.0 files.
Param: info
file info.
Param: info.fileName
file name.
Param: info.fileVersion
file version.
Param: info.fileRevision
file revision.
Param: info.description
What the file is for.
Param: info.creationDate
When the file was created.
Param: info.createdBy
Who created the file.
Param: info.vendorName
The device vendor name.
Param: info.vendorNumber
the device vendor number.
Param: info.productName
the device product name.
Param: info.productNumber
the device product number.
Param: info.revisionNumber
the device revision number.
Param: info.orderCode
the device order code.
Param: info.baudRates
supported buadrates
Param: info.lssSupported
true if LSS is supported.
See
CiA306 "Electronic data sheet specification for CANopen"