emitter.removeListener(eventName, listener)

• eventName <string> | <symbol>
• listener <Function>
• 返回: <EventEmitter>

从名为 eventName 的事件的监听器数组中移除指定的 listener。

const callback = (stream) => {
  console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);

removeListener() 最多从监听器数组中删除一个监听器实例。 如果任何单个监听器已多次添加到指定 eventName 的监听器数组中，则必须多次调用 removeListener() 以删除每个实例。

一旦事件被触发，则所有在触发时绑定到它的监听器都会被依次调用。 这意味着在触发之后和最后一个监听器完成执行之前的任何 removeListener() 或 removeAllListeners() 调用都不会从正在进行的 emit() 中删除它们。 后续事件按预期运行。

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 删除监听器 callbackB，但它仍将被调用。
// 触发时的内部监听器数组 [callbackA, callbackB]
myEmitter.emit('event');
// 打印:
//   A
//   B

// callbackB 现在被删除了。
// 内部监听器数组 [callbackA]
myEmitter.emit('event');
// 打印:
//   A

由于使用内部数组管理监听器，因此调用此方法将更改在移除监听器后注册的任何监听器的位置索引。 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() 方法返回的监听器数组的任何副本。

当单个函数被多次添加为单个事件的句柄时（如下例所示），则 removeListener() 将删除最近添加的实例。 在示例中，删除了 once('ping') 监听器：

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');

返回对 EventEmitter 的引用，以便可以链式调用。

• eventName <string> | <symbol>
• listener <Function>
• Returns: <EventEmitter>

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 from emit() in progress. Subsequent events behave as expected.

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:

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.