I'm storing an event listener inside a WeakMap and upon retrieving the function to remove it from the EventEmitter this error get's thrown:

TypeError: listener must be a function

I just can't figure out what the problem is:

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);

I'm storing an event listener inside a WeakMap and upon retrieving the function to remove it from the EventEmitter this error get's thrown:

TypeError: listener must be a function

I just can't figure out what the problem is:

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);

• javascript
• node.js
• eventemitter

• What is typeof listener in eventEmitterA.on('close', ...)? You have a console.log() if the typeof is function, but what is it actually there? – jfriend00 Commented Sep 10, 2015 at 22:06
• console.log(typeof listener) yields "function" – Olivenbaum Commented Sep 10, 2015 at 22:07
• 1 some docs might be helpful – Hacketo Commented Sep 10, 2015 at 22:08

1 Answer 1

eventEmitterB.removeListener(listener);

should be

eventEmitterB.removeListener('stuff', listener);

removeListener takes two arguments and the function is supposed to be the second argument, so you are passing the function as the name of the handler and undefined as the handler.