TypeError：listener必须是一个函数

Question

我将一个事件监听器存储在WeakMap中，并在检索该函数以将其从EventEmitter中删除时，会抛出此错误：

  

TypeError：listener必须是函数

我无法弄清问题是什么：

var EventEmitter = require('events').EventEmitter;

var listeners = new WeakMap();
var eventEmitterA = new EventEmitter();
var eventEmitterB = new EventEmitter();

eventEmitterA.on('open', (obj) => {
  function stuff() { /* ... */ }

  listeners.set(obj, stuff);

  eventEmitterB.on('stuff', stuff);
});

eventEmitterA.on('close', (obj) => {
  var listener = listeners.get(obj);

  console.log(typeof listener); // logs "function"

  eventEmitterB.removeListener(listener);
});


var someObject = {some: 'object'};

eventEmitterA.emit('open', someObject);
eventEmitterA.emit('close', someObject);