console.error is not a function

[jasnell]

Using 4.2.4 on OSX (not sure if this appears anywhere else yet).

Script: test.js

'use strict';
const EventEmitter = require('events');

EventEmitter.defaultMaxListeners = 1;

class MyEmitter extends EventEmitter {}

const myEmitter = new MyEmitter();
myEmitter.on('event', ()=>{});
myEmitter.on('event', ()=>{});

myEmitter.emit('event');

Output:

bash-3.2$ node ~/tmp/test.js
events.js:235
        console.error('(node) warning: possible EventEmitter memory ' +
                ^

TypeError: console.error is not a function
    at process.addListener (events.js:235:17)
    at process.stderr (node.js:652:17)
    at console.js:92:53
    at NativeModule.compile (node.js:954:5)
    at Function.NativeModule.require (node.js:902:18)
    at node.js:200:27
    at MyEmitter.addListener (events.js:235:9)
    at Object.<anonymous> (/Users/james/tmp/test.js:10:11)
    at Module._compile (module.js:435:26)
    at Object.Module._extensions..js (module.js:442:10)
bash-3.2$ 

[jasnell]

Same error does not occur using the repl:

bash-3.2$ node
> const EventEmitter = require('events');
undefined
> EventEmitter.defaultMaxListeners = 1
1
> class MyEmitter extends EventEmitter {}
[Function: MyEmitter]
> const myEmitter = new MyEmitter();
undefined
> myEmitter.on('event', ()=>{});
MyEmitter {
  domain: 
   Domain {
     domain: null,
     _events: { error: [Function] },
     _eventsCount: 1,
     _maxListeners: undefined,
     members: [] },
  _events: { event: [Function] },
  _eventsCount: 1,
  _maxListeners: undefined }
> myEmitter.on('event', ()=>{});
(node) warning: possible EventEmitter memory leak detected. 2 event listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
    at MyEmitter.addListener (events.js:239:17)
    at repl:1:11
    at REPLServer.defaultEval (repl.js:248:27)
    at bound (domain.js:287:14)
    at REPLServer.runBound [as eval] (domain.js:300:12)
    at REPLServer.<anonymous> (repl.js:412:12)
    at emitOne (events.js:82:20)
    at REPLServer.emit (events.js:169:7)
    at REPLServer.Interface._onLine (readline.js:210:10)
    at REPLServer.Interface._line (readline.js:549:8)
MyEmitter {
  domain: 
   Domain {
     domain: null,
     _events: { error: [Function] },
     _eventsCount: 1,
     _maxListeners: undefined,
     members: [] },
  _events: { event: [ [Function], [Function], warned: true ] },
  _eventsCount: 1,
  _maxListeners: undefined }
> 

[vkurchatkin]

Reproduces with:

const EventEmitter = require('events');
EventEmitter.defaultMaxListeners = 1;
console.error('');

console.error triggers some events. Documentation states:

This class property lets you set it for all EventEmitter instances, current and future, effective immediately. Use with care.

So this seems kind of expected.

[davidvgalbraith]

So, node sets up the global objects e.g. console lazily to make startup really fast. The second call to myEmitter.on('event', ()=>{}); in your test.js wants to trigger console.error with that big message about max listeners detected. So it has to initialize the global console.
The way these initializations work is they store an empty object as the global object, then eval the relevant file which fills in the properties of this object when it modifies module.exports. This is to prevent an infinite loop if you have a circular dependency.
But console.js does module.exports = new Console(process.stdout, process.stderr);, which references process.stdout and process.stderr, causing a call to the stdout and stderr getters on lines 660 and 675 of src/node.js, which both call

      if ((stdout / stderr).isTTY) {
        process.on('SIGWINCH', function() {

. The second one of these wants to trigger another warning about max listeners detected, so it has to initialize the global console. But there's already such an initialization in progress, which has cached an empty object in the global console, so this empty object is returned as the global console. An empty object doesn't have an error method, so you get this stack trace.

There's no problem in the REPL because stdout and stderr aren't TTY, so these SIGWINCH events aren't added to process.

I propose a fix at #4479.