WriteConcern can still be present on the options because we inherit options from the client/db/collection. The key must be present on the options in order to delete it. This allows typescript to delete the key but will not allow a writeConcern to be assigned as a property on options.WriteConcern仍然可以出现在选项上，因为我们从客户端/db/集合继承了选项。键必须存在于选项中才能删除。这允许typescript删除键，但不允许将writeConcern指定为选项的属性。
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.
Static ReadonlyCHANGEFired for each new matching change in the specified namespace. Attaching a 对于指定命名空间中的每个新匹配更改都会触发。将change event listener to a Change Stream will switch the stream into flowing mode. Data will then be passed as soon as it is available.change事件侦听器附加到更改流将使流切换到流动模式。数据一旦可用，就会立即传递。
Static ReadonlyCLOSEStaticdefaultBy 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. This limit can be changed for individual EventEmitter instances using the emitter.setMaxListeners(n) method. 10个侦听器。可以使用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. 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。However, calling 但是，调用emitter.setMaxListeners(n) still has precedence over events.defaultMaxListeners.emitter.setMaxListeners(n)仍然优先于events.defaultMaxListeners。
This is not a hard limit. 这不是一个硬性限制。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. 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.getMaxListeners()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 ReadonlyENDStatic ReadonlyERRORStatic 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 'error' event is emitted. Therefore, the process will still crash if no regular 'error' listener is installed.
Static ReadonlyINITStatic ReadonlyMOREStatic ReadonlyRESPONSEStatic ReadonlyRESUME_Emitted each time the change stream stores a new resume token.每次更改流存储新的恢复令牌时都会触发。
Is the cursor closed
The cached resume token that is used to resume after the most recently returned change.缓存的恢复令牌，用于在最近返回的更改后恢复。
Optional[captureRest...args: AnyRestAlias for emitter.on(eventName, listener).
Alias for emitter.on(eventName, listener).
Alias for emitter.on(eventName, listener).
Synchronously 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<ChangeStreamEvents<TSchema, TChange>[EventKey]>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().
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. 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. 默认情况下，事件侦听器按添加顺序调用。The 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. 默认情况下，事件侦听器按添加顺序调用。The 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. 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 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. No checks are made to see if the listener has already been added. 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。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和侦听器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. 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. 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.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. 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 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 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。
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。
Return a modified Readable stream including a possible transform method.返回一个修改后的Readable流，其中包含一个可能的转换方法。
NOTE: When using a Stream to process change stream events, the stream will NOT automatically resume in the case a resumable error is encountered.注意：当使用流处理更改流事件时，如果遇到可恢复的错误，流将不会自动恢复。
StaticaddListens once to the 在提供的abort event on the provided signal.signal上监听一次abort事件。
Listening to the 监听abort event on abort signals is unsafe and may lead to resource leaks since another third party with the signal can call e.stopImmediatePropagation(). abort信号上的中止事件是不安全的，可能会导致资源泄漏，因为另一个拥有该信号的第三方可以调用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.不幸的是，Node.js无法改变这一点，因为它违反了web标准。此外，最初的API使您很容易忘记删除侦听器。
This API allows safely using 这个API允许在Node.js API中安全地使用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.AbortSignal，方法是通过侦听事件来解决这两个问题，这样stopImmediatePropagation就不会阻止侦听器运行。
Returns a disposable so that it may be unsubscribed from more easily.返回一次性物品，以便更容易取消订阅。
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 一次性删除abort listener.abort侦听器。
StaticgetReturns 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。
For 对于EventEmitters this behaves exactly the same as calling .listeners on the emitter.EventEmitter，这与调用发射器上的.listeners完全相同。
For 对于EventTargets this is the only way to get the event listeners for the event target. This is useful for debugging and diagnostic purposes.EventTarget，这是获取事件目标的事件侦听器的唯一方法。这对于调试和诊断非常有用。
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.返回当前设置的最大侦听器数量。
For 对于EventEmitters this behaves exactly the same as calling .getMaxListeners on the emitter.EventEmitter，这与在发射器上调用.getMaxListeners的行为完全相同。
For 对于EventTargets this is the only way to get the max event listeners for the event target. EventTarget，这是获取事件目标的最大事件侦听器的唯一方法。If the number of event handlers on a single EventTarget exceeds the max set, the EventTarget will print a warning.如果单个EventTarget上的事件处理程序数量超过设置的最大值，EventTarget将打印警告。
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 一个类方法，返回在给定eventName registered on the given emitter.emitter上注册的给定eventName的侦听器数量。
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要查询的发射器
The event name事件名称
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 返回一个迭代AsyncIterator that iterates eventName events. eventName事件的AsyncIterator。It will throw if the 如果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.EventEmitter发出'error'，它将抛出。退出循环时，它会删除所有侦听器。每次迭代返回的value是由发出的事件参数组成的数组。
An AbortSignal can be used to cancel waiting on events:AbortSignal可用于取消等待事件：
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 使用close option to specify an array of event names that will end the iteration:close选项指定将结束迭代的事件名称数组：
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 一个非负数。每个EventTarget event.EventTarget事件的最大侦听器数。
Rest...eventTargets: (EventEmitter<DefaultEventMap> | EventTarget)[]
Zero or more {EventTarget} or {EventEmitter} instances. If none are specified, 零个或多个n is set as the default max for all newly created {EventTarget} and {EventEmitter} objects.{EventTarget}或{EventEmitter}实例。如果没有指定，则将n设置为所有新创建的{EventTarget}和{EventEmitter}对象的默认最大值。
Creates a new Change Stream instance. Normally created using Collection.watch().创建新的变更流实例。通常使用Collection.watch()创建。