node/test/parallel/test-event-emitter-check-listener-leaks.js

// Copyright Joyent, Inc. and other Node contributors.
//
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// persons to whom the Software is furnished to do so, subject to the
// following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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'use strict';

const common = require('../common');
const assert = require('assert');
const events = require('events');

// default
{
  const e = new events.EventEmitter();

  for (let i = 0; i < 10; i++) {
    e.on('default', common.mustNotCall());
  }
  assert.ok(!Object.hasOwn(e._events.default, 'warned'));
  e.on('default', common.mustNotCall());
  assert.ok(e._events.default.warned);

  // symbol
  const symbol = Symbol('symbol');
  e.setMaxListeners(1);
  e.on(symbol, common.mustNotCall());
  assert.ok(!Object.hasOwn(e._events[symbol], 'warned'));
  e.on(symbol, common.mustNotCall());
  assert.ok(Object.hasOwn(e._events[symbol], 'warned'));

  // specific
  e.setMaxListeners(5);
  for (let i = 0; i < 5; i++) {
    e.on('specific', common.mustNotCall());
  }
  assert.ok(!Object.hasOwn(e._events.specific, 'warned'));
  e.on('specific', common.mustNotCall());
  assert.ok(e._events.specific.warned);

  // only one
  e.setMaxListeners(1);
  e.on('only one', common.mustNotCall());
  assert.ok(!Object.hasOwn(e._events['only one'], 'warned'));
  e.on('only one', common.mustNotCall());
  assert.ok(Object.hasOwn(e._events['only one'], 'warned'));

  // unlimited
  e.setMaxListeners(0);
  for (let i = 0; i < 1000; i++) {
    e.on('unlimited', common.mustNotCall());
  }
  assert.ok(!Object.hasOwn(e._events.unlimited, 'warned'));
}

// process-wide
{
  events.EventEmitter.defaultMaxListeners = 42;
  const e = new events.EventEmitter();

  for (let i = 0; i < 42; ++i) {
    e.on('fortytwo', common.mustNotCall());
  }
  assert.ok(!Object.hasOwn(e._events.fortytwo, 'warned'));
  e.on('fortytwo', common.mustNotCall());
  assert.ok(Object.hasOwn(e._events.fortytwo, 'warned'));
  delete e._events.fortytwo.warned;

  events.EventEmitter.defaultMaxListeners = 44;
  e.on('fortytwo', common.mustNotCall());
  assert.ok(!Object.hasOwn(e._events.fortytwo, 'warned'));
  e.on('fortytwo', common.mustNotCall());
  assert.ok(Object.hasOwn(e._events.fortytwo, 'warned'));
}

// But _maxListeners still has precedence over defaultMaxListeners
{
  events.EventEmitter.defaultMaxListeners = 42;
  const e = new events.EventEmitter();
  e.setMaxListeners(1);
  e.on('uno', common.mustNotCall());
  assert.ok(!Object.hasOwn(e._events.uno, 'warned'));
  e.on('uno', common.mustNotCall());
  assert.ok(Object.hasOwn(e._events.uno, 'warned'));

  // chainable
  assert.strictEqual(e, e.setMaxListeners(1));
}