OptionalclusterOptionaloperationReadonlysnapshotOptional ExperimentaltimeoutMSSpecifies the time an operation in a given 指定给定ClientSession will run until it throws a timeout errorClientSession中的操作运行到抛出超时错误的时间
StaticcaptureValue: boolean
Change the default 更改所有新captureRejections option on all new EventEmitter objects.EventEmitter对象的默认captureRejections选项。
Static ReadonlycaptureValue: Symbol.for('nodejs.rejection')
See how to write a custom 了解如何编写自定义拒绝处理程序。rejection handler.
StaticdefaultBy default, a maximum of 默认情况下，任何单个事件最多可以注册10 listeners can be registered for any single event. 10个侦听器。This limit can be changed for individual 可以使用EventEmitter instances using the emitter.setMaxListeners(n) method. emitter.setMaxListeners(n)方法更改单个EventEmitter实例的此限制。To change the default for all要更改所有EventEmitter instances, the events.defaultMaxListeners property can be used. If this value is not a positive number, a RangeError is thrown.EventEmitter实例的默认值，可以使用events.defaultMaxListeners属性。如果此值不是正数，则抛出RangeError。
Take caution when setting the 设置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.events.defaultMaxListeners时要小心，因为更改会影响所有EventEmitter实例，包括在更改之前创建的实例。但是，调用emitter.setMaxListeners(n)仍然优先于events.defaultMaxListeners。
This is not a hard limit. The 这不是一个硬性限制。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. EventEmitter实例将允许添加更多侦听器，但会向stderr输出跟踪警告，指示已检测到“可能的EventEmitters内存泄漏”。For any single 对于任何单个EventEmitter, the emitter.getMaxListeners() and emitter.setMaxListeners() methods can be used to temporarily avoid this warning:EventEmitter，可以使用emitter.getMaxListener()和emitter.setMaxListeners()方法暂时避免此警告：
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.--trace warnings命令行标志可用于显示此类警告的堆栈跟踪。
The emitted warning can be inspected with 可以使用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. process.on('warning')检查发出的警告，并将具有额外的emitter、type和count属性，分别引用事件发射器实例、事件名称和附加侦听器的数量。Its 其name property is set to 'MaxListenersExceededWarning'.name属性设置为'MaxListenersExceededWarning'。
Static ReadonlyerrorThis symbol shall be used to install a listener for only monitoring 此符号应用于安装仅用于监视'error' events. 'error'事件的侦听器。Listeners installed using this symbol are called before the regular 使用此符号安装的侦听器在调用常规'error' listeners are called.'error'侦听器之前被调用。
Installing a listener using this symbol does not change the behavior once an 一旦发出'error' event is emitted. 'error'事件，使用此符号安装侦听器不会改变行为。Therefore, the process will still crash if no regular 因此，如果没有安装常规的'error' listener is installed.'error'侦听器，该进程仍将崩溃。
The server id associated with this session与此会话关联的服务器id
Experimental
An alias for ClientSession.endSession().
Optional[captureRest...args: AnyRestAlias for emitter.on(eventName, listener).
Alias for emitter.on(eventName, listener).
Alias for emitter.on(eventName, listener).
Advances the clusterTime for a ClientSession to the provided clusterTime of another ClientSession将ClientSession的clusterTime提前到另一个ClientSession的提供clusterTime
the $clusterTime returned by the server from another session in the form of a document containing the 服务器以包含BSON.Timestamp clusterTime and signatureBSON.Timestamp clusterTime和签名的文档形式从另一个会话返回的$clusterTime
Advances the operationTime for a ClientSession.提前ClientSession的操作时间。
the 希望前进到的操作类型的BSON.Timestamp of the operation type it is desired to advance toBSON.Timestamp
Commits the currently active transaction in this session.提交此会话中当前活动的事务。
Optionaloptions: { Optional options, can be used to override 可选选项，可用于覆盖defaultTimeoutMS.defaultTimeoutMS。
OptionaltimeoutMS?: numberSynchronously calls each of the listeners registered for the event named 按照注册顺序同步调用为名为eventName, in the order they were registered, passing the supplied arguments to each.eventName的事件注册的每个侦听器，并将提供的参数传递给每个侦听器。
Returns 如果事件有侦听器，则返回true if the event had listeners, false otherwise.true，否则返回false。
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
Rest...args: Parameters<ClientSessionEvents[EventKey]>Frees any client-side resources held by the current session. If a session is in a transaction, the transaction is aborted.释放当前会话所占用的任何客户端资源。如果会话在事务中，则事务中止。
Does not end the session on the server.不会结束服务器上的会话。
Optionaloptions: EndSessionOptions
Optional settings. Currently reserved for future use可选设置。目前保留供将来使用
Used to determine if this session equals another用于确定此会话是否等于另一个会话
The session to compare to要比较的会话
Returns an array listing the events for which the emitter has registered listeners. The values in the array are strings or 返回一个数组，列出发射器已注册侦听器的事件。数组中的值是字符串或Symbols.Symbol。
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 the current max listener value for the 返回EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to EventEmitter.defaultMaxListeners.EventEmitter的当前最大侦听器值，该值由emitter.setMaxListeners(n)设置或默认为EventEmitter.defaultMaxListeners。
Returns the number of listeners listening for the event named 返回侦听名为eventName. eventName的事件的侦听器数量。If 如果提供了listener is provided, it will return how many times the listener is found in the list of the listeners of the event.listener，它将返回在事件监听器列表中找到监听器的次数。
Returns a copy of the array of listeners for the event named 返回名为eventName.eventName的事件的侦听器数组的副本。
server.on('connection', (stream) => {
console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
Alias for emitter.removeListener().emitter.removeListener()的别名。
Alias for emitter.removeListener().
Alias for emitter.removeListener().
Adds the 将listener function to the end of the listeners array for the event named eventName. listener函数添加到名为eventName的事件的侦听器数组末尾。No checks are made to see if the 不检查是否已添加listener has already been added. listener。Multiple calls passing the same combination of 传递相同eventName and listener will result in the listener being added, and called, multiple times.eventName和listener组合的多个调用将导致listener被多次添加和调用。
server.on('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
By default, event listeners are invoked in the order they are added. The 默认情况下，事件侦听器按添加顺序调用。emitter.prependListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.emitter.prependListener()方法可以用作将事件侦听器添加到侦听器数组开头的替代方法。
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
The callback function回调函数
Adds the 将listener function to the end of the listeners array for the event named eventName. listener函数添加到名为eventName的事件的侦听器数组末尾。No checks are made to see if the 不检查是否已添加listener has already been added. listener。Multiple calls passing the same combination of 传递相同eventName and listener will result in the listener being added, and called, multiple times.eventName和listener组合的多个调用将导致listener被多次添加和调用。
server.on('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
By default, event listeners are invoked in the order they are added. The 默认情况下，事件侦听器按添加顺序调用。emitter.prependListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.emitter.prependListener()方法可以用作将事件侦听器添加到侦听器数组开头的替代方法。
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
The callback function回调函数
Adds the 将listener function to the end of the listeners array for the event named eventName. listener函数添加到名为eventName的事件的侦听器数组末尾。No checks are made to see if the 不检查是否已添加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.listener。传递相同eventName和listener组合的多个调用将导致listener被多次添加和调用。
server.on('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
By default, event listeners are invoked in the order they are added. The 默认情况下，事件侦听器按添加顺序调用。emitter.prependListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.emitter.prependListener()方法可以用作将事件侦听器添加到侦听器数组开头的替代方法。
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
The callback function回调函数
Adds a one-time 为名为listener function for the event named eventName. eventName的事件添加一次性listener函数。The next time 下次触发eventName is triggered, this listener is removed and then invoked.eventName时，将删除并调用此侦听器。
server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
By default, event listeners are invoked in the order they are added. The 默认情况下，事件侦听器按添加顺序调用。emitter.prependOnceListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.emitter.prependOnceListener()方法可以用作将事件侦听器添加到侦听器数组开头的替代方法。
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
The callback function回调函数
Adds a one-time 为名为listener function for the event named eventName. The next time eventName is triggered, this listener is removed and then invoked.eventName的事件添加一次性listener函数。下次触发eventName时，将删除并调用此listener。
server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
By default, event listeners are invoked in the order they are added. 默认情况下，事件侦听器按添加顺序调用。The emitter.prependOnceListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.emitter.prependOnceListener()方法可以用作将事件侦听器添加到侦听器数组开头的替代方法。
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
The callback function回调函数
Adds a one-time 为名为listener function for the event named eventName. The next time eventName is triggered, this listener is removed and then invoked.eventName的事件添加一次性listener函数。下次触发eventName时，将删除并调用此listener。
server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
By default, event listeners are invoked in the order they are added. The 默认情况下，事件侦听器按添加顺序调用。emitter.prependOnceListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.emitter.prependOnceListener()方法可以用作将事件侦听器添加到侦听器数组开头的替代方法。
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
The callback function回调函数
Adds the 将listener function to the beginning of the listeners array for the event named eventName. listener函数添加到名为eventName的事件的侦听器数组的开头。No checks are made to see if the 不检查是否已添加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.listener。传递相同eventName和listener组合的多个调用将导致listener被多次添加和调用。
server.prependListener('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
The callback function回调函数
Adds the 将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.listener函数添加到名为eventName的事件的侦听器数组的开头。不检查是否已添加侦听器。传递相同eventName和listener组合的多个调用将导致侦听器被多次添加和调用。
server.prependListener('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
The callback function回调函数
Adds the 将listener function to the beginning of the listeners array for the event named eventName. listener函数添加到名为eventName的事件的侦听器数组的开头。No checks are made to see if the 不检查是否已添加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.listener。传递相同eventName和listener组合的多个调用将导致listener被多次添加和调用。
server.prependListener('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
The callback function回调函数
Adds a one-time将名为listener function for the event named eventName to the beginning of the listeners array. eventName的事件的一次性listener函数添加到侦听器数组的开头。The next time 下次触发eventName is triggered, this listener is removed, and then invoked.eventName时，此侦听器将被删除，然后被调用。
server.prependOnceListener('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
The callback function回调函数
Adds a one-time将名为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.eventName的事件的一次性listener函数添加到侦听器数组的开头。下次触发eventName时，此listener将被删除，然后被调用。
server.prependOnceListener('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
The callback function回调函数
Adds a one-time将名为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.eventName的事件的一次性listener函数添加到侦听器数组的开头。下次触发eventName时，此listener将被删除，然后被调用。
server.prependOnceListener('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
The callback function回调函数
Returns a copy of the array of listeners for the event named 返回名为eventName, including any wrappers (such as those created by .once()).eventName的事件的侦听器数组的副本，包括任何包装器（如.once()创建的包装器）。
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 删除所有侦听器或指定eventName.eventName的侦听器。
It is bad practice to remove listeners added elsewhere in the code, particularly when the 删除代码中其他地方添加的监听器是不好的做法，特别是当EventEmitter instance was created by some other component or module (e.g. sockets or file streams).EventEmitter实例是由其他组件或模块（例如套接字或文件流）创建的时候。
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
Optionalevent: string | symbol | EventKeyRemoves the specified 从名为listener from the listener array for the event named eventName.eventName的事件的侦听器数组中删除指定的listener。
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. 将从侦听器数组中最多删除一个侦听器实例。If any single listener has been added multiple times to the listener array for the specified 如果任何单个侦听器已多次添加到指定eventName, then removeListener() must be called multiple times to remove each instance.eventName的侦听器数组中，则必须多次调用removeListener()以删除每个实例。
Once an event is emitted, all listeners attached to it at the time of emitting are called in order. 一旦事件被发出，在发出时附加到它的所有侦听器都会按顺序被调用。This implies that any 这意味着在发出之后和最后一个监听器完成执行之前的任何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.removeListener()或removeAllListeners()调用都不会将它们从正在进行的emit()中删除。后续事件按预期进行。
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. 由于侦听器是使用内部数组管理的，因此调用此函数将更改删除侦听器后注册的任何侦听器的位置索引。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 这不会影响调用监听器的顺序，但这意味着需要重新创建emitter.listeners() method will need to be recreated.emitter.listeners()方法返回的监听器数组的任何副本。
When a single function has been added as a handler multiple times for a single event (as in the example below), 当一个函数被多次添加为单个事件的处理程序时（如下例所示），removeListener() will remove the most recently added instance. removeListener()将删除最近添加的实例。In the example the 在该示例中，once('ping') listener is removed:once('ping')监听器被删除：
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 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
Removes the specified 从名为listener from the listener array for the event named eventName.eventName的事件的侦听器数组中删除指定的listener。
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. 将从侦听器数组中最多删除一个侦听器实例。If any single listener has been added multiple times to the listener array for the specified 如果任何单个侦听器已多次添加到指定eventName, then removeListener() must be called multiple times to remove each instance.eventName的侦听器数组中，则必须多次调用removeListener()以删除每个实例。
Once an event is emitted, all listeners attached to it at the time of emitting are called in order. 一旦事件被发出，在发出时附加到它的所有侦听器都会按顺序被调用。This implies that any 这意味着在发出之后和最后一个监听器完成执行之前的任何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.removeListener()或removeAllListeners()调用都不会将它们从正在进行的emit()中删除。后续事件按预期进行。
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. 由于侦听器是使用内部数组管理的，因此调用此函数将更改删除侦听器后注册的任何侦听器的位置索引。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 这不会影响调用监听器的顺序，但这意味着需要重新创建emitter.listeners() method will need to be recreated.emitter.listeners()方法返回的监听器数组的任何副本。
When a single function has been added as a handler multiple times for a single event (as in the example below), 当一个函数被多次添加为单个事件的处理程序时（如下例所示），removeListener() will remove the most recently added instance. In the example the once('ping') listener is removed:removeListener()将删除最近添加的实例。在该示例中，once('ping')监听器被删除：
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 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
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. 将从侦听器数组中最多删除一个侦听器实例。If any single listener has been added multiple times to the listener array for the specified 如果任何单个侦听器已多次添加到指定eventName, then removeListener() must be called multiple times to remove each instance.eventName的侦听器数组中，则必须多次调用removeListener()以删除每个实例。
Once an event is emitted, all listeners attached to it at the time of emitting are called in order. 一旦事件被发出，在发出时附加到它的所有侦听器都会按顺序被调用。This implies that any 这意味着在发出之后和最后一个监听器完成执行之前的任何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.removeListener()或removeAllListeners()调用都不会将它们从正在进行的emit()中删除。后续事件按预期进行。
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 由于侦听器是使用内部数组管理的，因此调用此函数将更改删除侦听器后注册的任何侦听器的位置索引。这不会影响调用监听器的顺序，但这意味着需要重新创建emitter.listeners() method will need to be recreated.emitter.listeners()方法返回的监听器数组的任何副本。
When a single function has been added as a handler multiple times for a single event (as in the example below), 当一个函数被多次添加为单个事件的处理程序时（如下例所示），removeListener() will remove the most recently added instance. In the example the once('ping') listener is removed:removeListener()将删除最近添加的实例。在该示例中，once('ping')监听器被删除：
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 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
By default 默认情况下，如果为特定事件添加了EventEmitters will print a warning if more than 10 listeners are added for a particular event. 10个以上的监听器，EventEmitter将打印警告。This is a useful default that helps finding memory leaks. 这是一个有用的默认值，有助于查找内存泄漏。The emitter.setMaxListeners() method allows the limit to be modified for this specific EventEmitter instance. emitter.setMaxListeners()方法允许修改此特定EventEmitter实例的限制。The value can be set to 该值可以设置为Infinity (or 0) to indicate an unlimited number of listeners.Infinity（或0），以表示侦听器的数量不受限制。
Returns a reference to the 返回对EventEmitter, so that calls can be chained.EventEmitter的引用，以便可以链接调用。
Starts a new transaction with the given options.使用给定的选项开始新的事务。
Optionaloptions: TransactionOptions
Options for the transaction
Starts a transaction and runs a provided function, ensuring the commitTransaction is always attempted when all operations run in the function have completed.启动事务并运行提供的函数，确保在函数中运行的所有操作都已完成时始终尝试commitTransaction。
IMPORTANT: This method requires the function passed in to return a Promise. That promise must be made by 此方法要求传入的函数返回Promise。这个promise必须通过等待所有操作来实现，这样拒绝就会传播到返回的promise。await-ing all operations in such a way that rejections are propagated to the returned promise.
IMPORTANT: Running operations in parallel is not supported during a transaction. The use of 事务期间不支持并行运行操作。使用Promise.all, Promise.allSettled, Promise.race, etc to parallelize operations inside a transaction is undefined behaviour.Promise.all、Promise.allSettled、Promise.race等在事务中并行化操作是未定义的行为。
IMPORTANT: When running an operation inside a 在withTransaction callback, if it is not provided the explicit session in its options, it will not be part of the transaction and it will not respect timeoutMS.withTransaction回调中运行操作时，如果在其选项中没有提供显式会话，则该操作将不会成为事务的一部分，也不会遵守超时MS。
callback to run within a transaction回调在事务中运行
Optionaloptions: TransactionOptions & { optional settings for the transaction事务的可选设置
A raw command response or undefined
commitTransaction operation is successful, then the provided function will return the result of the provided function.Checkout a descriptive example here:
https://www.mongodb.com/blog/post/quick-start-nodejs--mongodb--how-to-implement-transactions
If a command inside withTransaction fails:
To avoid this situation, the application must not silently handle errors within the provided function. If the application needs to handle errors within, it must await all operations such that if an operation is rejected it becomes the rejection of the callback function passed into withTransaction.
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.
StaticgetReturns 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
}
StaticlistenerA 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
Optionaloptions: StaticEventEmitterIteratorOptionsStaticonceCreates 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: StaticEventEmitterOptionsOptionaloptions: StaticEventEmitterOptionsStaticsetimport { setMaxListeners, EventEmitter } from 'node:events';
const target = new EventTarget();
const emitter = new EventEmitter();
setMaxListeners(5, target, emitter);
Optionaln: number
A non-negative number. The maximum number of listeners per EventTarget event.
Rest...eventTargets: (EventEmitter<DefaultEventMap> | EventTarget)[]
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 class representing a client session on the server表示服务器上客户端会话的类NOTE: not meant to be instantiated directly.注意：不打算直接实例化。