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

// Copyright Joyent, Inc. and other Node contributors.
//
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// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
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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.
//
// 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 OR OTHER DEALINGS IN THE SOFTWARE.

'use strict';

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

let e = new events.EventEmitter();

// default
for (let i = 0; i < 10; i++) {
  e.on('default', common.noop);
}
assert.ok(!e._events['default'].hasOwnProperty('warned'));
e.on('default', common.noop);
assert.ok(e._events['default'].warned);

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

// specific
e.setMaxListeners(5);
for (let i = 0; i < 5; i++) {
  e.on('specific', common.noop);
}
assert.ok(!e._events['specific'].hasOwnProperty('warned'));
e.on('specific', common.noop);
assert.ok(e._events['specific'].warned);

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

// unlimited
e.setMaxListeners(0);
for (let i = 0; i < 1000; i++) {
  e.on('unlimited', common.noop);
}
assert.ok(!e._events['unlimited'].hasOwnProperty('warned'));

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

for (let i = 0; i < 42; ++i) {
  e.on('fortytwo', common.noop);
}
assert.ok(!e._events['fortytwo'].hasOwnProperty('warned'));
e.on('fortytwo', common.noop);
assert.ok(e._events['fortytwo'].hasOwnProperty('warned'));
delete e._events['fortytwo'].warned;

events.EventEmitter.defaultMaxListeners = 44;
e.on('fortytwo', common.noop);
assert.ok(!e._events['fortytwo'].hasOwnProperty('warned'));
e.on('fortytwo', common.noop);
assert.ok(e._events['fortytwo'].hasOwnProperty('warned'));

// but _maxListeners still has precedence over defaultMaxListeners
events.EventEmitter.defaultMaxListeners = 42;
e = new events.EventEmitter();
e.setMaxListeners(1);
e.on('uno', common.noop);
assert.ok(!e._events['uno'].hasOwnProperty('warned'));
e.on('uno', common.noop);
assert.ok(e._events['uno'].hasOwnProperty('warned'));

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