AbstractProtectedsignalStaticcaptureStatic 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 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. 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. 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. 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. Its name property is set to 'MaxListenersExceededWarning'.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。其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. Listeners installed using this symbol are called before the regular 'error' listeners are called.'error'事件的侦听器。使用此符号安装的侦听器在调用常规'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. Therefore, the process will still crash if no regular 'error' listener is installed.'error'事件，使用此符号安装侦听器不会改变行为。因此，如果没有安装常规的'error'侦听器，该进程仍将崩溃。
The cursor is closed and all remaining locally buffered documents have been iterated.游标关闭，所有剩余的本地缓冲文档都已迭代。
The cursor has no id until it receives a response from the initial cursor creating command.游标在收到初始游标创建命令的响应之前没有id。
It is non-zero for as long as the database has an open cursor.只要数据库有一个打开的游标，它就是非零的。
The initiating command may receive a zero id if the entire result is in the 如果整个结果在firstBatch.firstBatch中，则启动命令可能会收到一个零id。
A 试图在此游标上执行killCursors command was attempted on this cursor. This is performed if the cursor id is non zero.killCursors命令。如果游标id不为零，则执行此操作。
Experimental
An alias for AbstractCursor.close().AbstractCursor.close()的别名。
Optional[captureRest...args: AnyRestAdd a cursor flag to the cursor向游标添加游标标志
The flag to set, must be one of following ['tailable', 'oplogReplay', 'noCursorTimeout', 'awaitData', 'partial'].要设置的标志必须是以下之一['tailable', 'oplogReplay', 'noCursorTimeout', 'awaitData', 'partial']。
The flag boolean value.标志的布尔值。
Alias for emitter.on(eventName, listener).emitter.on(eventName, listener)的别名。
Alias for emitter.on(eventName, listener).emitter.on(eventName, listener)的别名。
Alias for emitter.on(eventName, listener).emitter.on(eventName, listener)的别名。
Set the batch size for the cursor.设置游标的批量大小。
The number of documents to return per batch. See command documentation.每批要返回的文档数量。请参阅命令文档。
AbstractcloneReturns a new uninitialized copy of this cursor, with options matching those that have been set on the current instance返回此游标的新的未初始化副本，其中包含与当前实例上设置的选项匹配的选项
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<CursorEvents[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. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.eventName的事件的侦听器数量。如果提供了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] ]
Map all documents using the provided function If there is a transform set on the cursor, that will be called first and the result passed to this function's transform.使用提供的函数映射所有文档如果游标上有一个转换集，则将首先调用该转换集，并将结果传递给此函数的转换。
Note Cursors use 游标在内部使用null internally to indicate that there are no more documents in the cursor. Providing a mapping function that maps values to null will result in the cursor closing itself before it has finished iterating all documents. null表示游标中没有更多文档。提供一个将值映射为null的映射函数将导致游标在完成所有文档的迭代之前自动关闭。This will not result in a memory leak, just surprising behavior. For example:这不会导致内存泄漏，只是令人惊讶的行为。例如：
const cursor = collection.find({});
cursor.map(() => null);
const documents = await cursor.toArray();
// documents is always [], regardless of how many documents are in the collection.
Other falsey values are allowed:
const cursor = collection.find({});
cursor.map(() => '');
const documents = await cursor.toArray();
// documents is now an array of empty strings
Note for Typescript Users: adding a transform changes the return type of the iteration of this cursor, it does not return a new instance of a cursor. 添加转换会更改此游标迭代的返回类型，它不会返回游标的新实例。This means when calling map, you should always assign the result to a new variable in order to get a correctly typed cursor variable. Take note of the following example:这意味着在调用map时，您应该始终将结果分配给一个新变量，以便获得正确类型的游标变量。请注意以下示例：
const cursor: FindCursor<Document> = coll.find();
const mappedCursor: FindCursor<number> = cursor.map(doc => Object.keys(doc).length);
const keyCounts: number[] = await mappedCursor.toArray(); // cursor.toArray() still returns Document[]
Set a maxTimeMS on the cursor query, allowing for hard timeout limits on queries (Only supported on MongoDB 2.6 or higher)在游标查询上设置maxTimeMS，允许对查询进行硬超时限制（仅在MongoDB 2.6或更高版本上支持）
Number of milliseconds to wait before aborting the query.中止查询前等待的毫秒数。
Alias for emitter.removeListener().emitter.removeListener()的别名。
Alias for emitter.removeListener().emitter.removeListener()的别名。
Alias for emitter.removeListener().emitter.removeListener()的别名。
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 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. 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. 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. 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 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-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 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 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.
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.
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.
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.
Returns an array of documents. The caller is responsible for making sure that there is enough memory to store the results. Note that the array only contains partial results when this cursor had been previously accessed. In that case, cursor.rewind() can be used to reset the cursor.
Set the ReadPreference for the cursor.
Set the ReadPreference for the cursor.
The new read preference for the cursor.
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.
Value: boolean
Change the default更改所有新captureRejectionsoption on all newEventEmitterobjects.EventEmitter对象的默认captureRejections选项。