node/test/parallel/test-eventtarget-memoryleakwarning.js

// Flags: --no-warnings
'use strict';
const common = require('../common');
const {
  setMaxListeners,
  EventEmitter
} = require('events');
const assert = require('assert');

common.expectWarning({
  MaxListenersExceededWarning: [
    ['Possible EventTarget memory leak detected. 3 foo listeners added to ' +
     'EventTarget. Use events.setMaxListeners() ' +
     'to increase limit'],
    ['Possible EventTarget memory leak detected. 3 foo listeners added to ' +
     '[MessagePort [EventTarget]]. ' +
     'Use events.setMaxListeners() to increase ' +
     'limit'],
    ['Possible EventTarget memory leak detected. 3 foo listeners added to ' +
     '[MessagePort [EventTarget]]. ' +
     'Use events.setMaxListeners() to increase ' +
     'limit'],
    ['Possible EventTarget memory leak detected. 3 foo listeners added to ' +
     '[AbortSignal]. ' +
     'Use events.setMaxListeners() to increase ' +
     'limit'],
  ],
});


{
  const et = new EventTarget();
  setMaxListeners(2, et);
  et.addEventListener('foo', () => {});
  et.addEventListener('foo', () => {});
  et.addEventListener('foo', () => {});
}

{
  // No warning emitted because prior limit was only for that
  // one EventTarget.
  const et = new EventTarget();
  et.addEventListener('foo', () => {});
  et.addEventListener('foo', () => {});
  et.addEventListener('foo', () => {});
}

{
  const mc = new MessageChannel();
  setMaxListeners(2, mc.port1);
  mc.port1.addEventListener('foo', () => {});
  mc.port1.addEventListener('foo', () => {});
  mc.port1.addEventListener('foo', () => {});
}

{
  // Set the default for newly created EventTargets
  setMaxListeners(2);
  const mc = new MessageChannel();
  mc.port1.addEventListener('foo', () => {});
  mc.port1.addEventListener('foo', () => {});
  mc.port1.addEventListener('foo', () => {});

  const ac = new AbortController();
  ac.signal.addEventListener('foo', () => {});
  ac.signal.addEventListener('foo', () => {});
  ac.signal.addEventListener('foo', () => {});
}

{
  // It works for EventEmitters also
  const ee = new EventEmitter();
  setMaxListeners(2, ee);
  assert.strictEqual(ee.getMaxListeners(), 2);
}