All files / lib/internal event_target.js

100% Statements 853/853
97.96% Branches 240/245
100% Functions 61/61
100% Lines 853/853

Press n or j to go to the next uncovered block, b, p or k for the previous block.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 85438x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 3x 3x 38x 38x 66189x 66189x 66189x 38x 38x 38x 33129x 33129x 33127x 33127x 33127x 33127x 33127x 33127x 33127x 33127x 33127x 33127x 33127x 33129x 348x 348x 33123x 33123x 33123x 33123x 33123x 33123x 33123x 33123x 33123x 33129x 38x 38x 2x 2x 2x 2x 2x 1x 1x 2x 2x 2x 2x 2x 2x 2x 2x 2x 2x 38x 38x 4x 4x 3x 4x 38x 38x 7x 7x 6x 7x 38x 38x 11x 11x 10x 11x 38x 38x 2x 2x 1x 2x 38x 38x 2x 2x 1x 2x 38x 38x 33074x 33074x 33073x 33074x 38x 38x 4x 4x 3x 4x 38x 38x 33032x 33032x 33032x 33032x 38x 38x 2x 2x 1x 2x 38x 38x 38x 38x 38x 38x 38x 6x 6x 6x 6x 38x 38x 2x 2x 1x 2x 38x 38x 4x 4x 3x 4x 38x 38x 2x 2x 1x 2x 38x 38x 10x 10x 10x 10x 38x 38x 14x 14x 13x 14x 38x 38x 4x 4x 4x 4x 4x 4x 38x 38x 7x 7x 6x 7x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 2x 2x 2x 2x 2x 38x 38x 38x 38x 38x 38x 38x 38x 45x 45x 45x 45x 45x 45x 45x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 110968x 110968x 110968x 110968x 110968x 110968x 110968x 110968x 110968x 110968x 110968x 110968x 110968x 110968x 110968x 16x 16x 16x 16x 16x 110968x 110945x 110945x 110952x 7x 7x 7x 110968x 38x 38x 20232x 20232x 20232x 38x 38x 40283x 40283x 40283x 40283x 40283x 40283x 40283x 40283x 38x 38x 35371x 35371x 35371x 35371x 35371x 38x 38x 38x 38x 38x 38x 38x 38x 1599x 1599x 38x 38x 110970x 110970x 110970x 5x 5x 5x 5x 5x 5x 5x 5x 5x 5x 5x 5x 5x 110970x 38x 38x 38x 110991x 110991x 110990x 110990x 110988x 110988x 110988x 110988x 110988x 110988x 110988x 110988x 110988x 110988x 110988x 110988x 110990x 5x 5x 5x 5x 5x 5x 5x 5x 5x 5x 5x 110973x 110973x 110990x 13x 1x 1x 12x 12x 12x 10x 12x 12x 110972x 110972x 110972x 110989x 100920x 100920x 100920x 100920x 100920x 100920x 100920x 100920x 10052x 10052x 10052x 10052x 10052x 110991x 56x 56x 56x 10052x 80319x 4x 4x 10048x 10048x 10048x 10048x 10048x 110991x 38x 38x 20225x 20225x 20224x 20224x 20219x 20219x 20225x 20225x 20225x 20225x 20225x 20171x 20171x 20175x 20172x 20164x 20164x 20164x 20164x 20164x 20164x 20164x 8x 8x 20225x 38x 38x 33036x 33036x 33026x 33026x 33035x 33021x 33021x 33035x 33020x 33020x 33020x 33020x 33036x 38x 38x 91026x 264x 73x 73x 73x 73x 264x 91026x 91026x 33020x 33020x 33020x 91026x 91026x 91026x 91026x 58204x 58204x 58204x 58204x 58250x 91026x 58231x 58231x 58231x 58231x 2x 2x 2x 2x 2x 58231x 20117x 20117x 20117x 20117x 20117x 58229x 58229x 58229x 58231x 57965x 58225x 264x 264x 58231x 58231x 58231x 58231x 58228x 58228x 261x 261x 58228x 58231x 58231x 58231x 43x 43x 58205x 58205x 58205x 58180x 58180x 90780x 91026x 38x 38x 2x 2x 38x 3x 3x 3x 3x 3x 1x 1x 3x 3x 3x 3x 3x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 33772x 33772x 33772x 38x 38x 38x 38x 38x 38x 13x 13x 13x 38x 38x 2x 2x 1x 2x 38x 38x 2x 2x 1x 2x 38x 38x 8x 8x 7x 8x 38x 38x 28x 28x 27x 28x 28x 38x 38x 80x 80x 79x 79x 80x 38x 38x 20010x 20010x 20009x 20009x 20010x 38x 38x 70566x 70566x 70565x 70565x 70566x 38x 38x 4x 4x 3x 3x 4x 38x 4x 4x 3x 3x 3x 3x 4x 38x 38x 40063x 40063x 40062x 40062x 40062x 40063x 38x 38x 3x 3x 2x 1x 1x 1x 1x 2x 2x 3x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 131212x 131212x 131212x 131192x 131192x 20x 20x 71x 10x 10x 131212x 38x 110988x 110988x 110988x 110987x 110987x 110988x 110986x 110986x 110986x 110986x 110986x 110986x 110986x 110986x 110986x 110986x 110986x 110988x 38x 38x 38x 38x 38x 38x 164311x 164311x 164311x 38x 130770x 130770x 130770x 38x 13620x 13620x 13620x 3x 2x 2x 2x 3x 3x 13620x 38x 45x 45x 45x 38x 129x 129x 129x 129x 94x 1x 1x 93x 94x 129x 129x 129x 38x 2831x 2831x 2831x 2831x 1x 2831x 2831x 133x 89x 89x 133x 133x 4x 4x 4x 4x 4x 4x 4x 2x 2x 2x 2x 133x 129x 129x 129x 133x 2831x 2831x 2831x 2831x 2831x 38x 38x 5371x 5371x 541x 541x 541x 541x 5371x 5371x 5371x 5371x 5371x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x 38x  
'use strict';
 
const {
  ArrayFrom,
  Boolean,
  Error,
  FunctionPrototypeBind,
  FunctionPrototypeCall,
  NumberIsInteger,
  ObjectAssign,
  ObjectCreate,
  ObjectDefineProperties,
  ObjectDefineProperty,
  ObjectGetOwnPropertyDescriptor,
  ObjectGetOwnPropertyDescriptors,
  ReflectApply,
  SafeArrayIterator,
  SafeFinalizationRegistry,
  SafeMap,
  SafeWeakMap,
  SafeWeakRef,
  SafeWeakSet,
  String,
  Symbol,
  SymbolFor,
  SymbolToStringTag,
} = primordials;
 
const {
  codes: {
    ERR_INVALID_ARG_TYPE,
    ERR_EVENT_RECURSION,
    ERR_MISSING_ARGS,
    ERR_INVALID_THIS,
  }
} = require('internal/errors');
const { validateObject, validateString } = require('internal/validators');
 
const { customInspectSymbol } = require('internal/util');
const { inspect } = require('util');
 
const kIsEventTarget = SymbolFor('nodejs.event_target');
const kIsNodeEventTarget = Symbol('kIsNodeEventTarget');
 
const EventEmitter = require('events');
const {
  kMaxEventTargetListeners,
  kMaxEventTargetListenersWarned,
} = EventEmitter;
 
const kEvents = Symbol('kEvents');
const kIsBeingDispatched = Symbol('kIsBeingDispatched');
const kStop = Symbol('kStop');
const kTarget = Symbol('kTarget');
const kHandlers = Symbol('khandlers');
const kWeakHandler = Symbol('kWeak');
 
const kHybridDispatch = SymbolFor('nodejs.internal.kHybridDispatch');
const kCreateEvent = Symbol('kCreateEvent');
const kNewListener = Symbol('kNewListener');
const kRemoveListener = Symbol('kRemoveListener');
const kIsNodeStyleListener = Symbol('kIsNodeStyleListener');
const kTrustEvent = Symbol('kTrustEvent');
 
const { now } = require('internal/perf/utils');
 
// TODO(joyeecheung): V8 snapshot does not support instance member
// initializers for now:
// https://bugs.chromium.org/p/v8/issues/detail?id=10704
const kType = Symbol('type');
const kDefaultPrevented = Symbol('defaultPrevented');
const kCancelable = Symbol('cancelable');
const kTimestamp = Symbol('timestamp');
const kBubbles = Symbol('bubbles');
const kComposed = Symbol('composed');
const kPropagationStopped = Symbol('propagationStopped');
 
const isTrustedSet = new SafeWeakSet();
const isTrusted = ObjectGetOwnPropertyDescriptor({
  get isTrusted() {
    return isTrustedSet.has(this);
  }
}, 'isTrusted').get;
 
function isEvent(value) {
  return typeof value?.[kType] === 'string';
}
 
class Event {
  constructor(type, options = null) {
    if (arguments.length === 0)
      throw new ERR_MISSING_ARGS('type');
    validateObject(options, 'options', {
      allowArray: true, allowFunction: true, nullable: true,
    });
    const { cancelable, bubbles, composed } = { ...options };
    this[kCancelable] = !!cancelable;
    this[kBubbles] = !!bubbles;
    this[kComposed] = !!composed;
    this[kType] = `${type}`;
    this[kDefaultPrevented] = false;
    this[kTimestamp] = now();
    this[kPropagationStopped] = false;
    if (options?.[kTrustEvent]) {
      isTrustedSet.add(this);
    }
 
    // isTrusted is special (LegacyUnforgeable)
    ObjectDefineProperty(this, 'isTrusted', {
      get: isTrusted,
      enumerable: true,
      configurable: false
    });
    this[kTarget] = null;
    this[kIsBeingDispatched] = false;
  }
 
  [customInspectSymbol](depth, options) {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    const name = this.constructor.name;
    if (depth < 0)
      return name;
 
    const opts = ObjectAssign({}, options, {
      depth: NumberIsInteger(options.depth) ? options.depth - 1 : options.depth
    });
 
    return `${name} ${inspect({
      type: this[kType],
      defaultPrevented: this[kDefaultPrevented],
      cancelable: this[kCancelable],
      timeStamp: this[kTimestamp],
    }, opts)}`;
  }
 
  stopImmediatePropagation() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    this[kStop] = true;
  }
 
  preventDefault() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    this[kDefaultPrevented] = true;
  }
 
  get target() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kTarget];
  }
 
  get currentTarget() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kTarget];
  }
 
  get srcElement() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kTarget];
  }
 
  get type() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kType];
  }
 
  get cancelable() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kCancelable];
  }
 
  get defaultPrevented() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kCancelable] && this[kDefaultPrevented];
  }
 
  get timeStamp() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kTimestamp];
  }
 
 
  // The following are non-op and unused properties/methods from Web API Event.
  // These are not supported in Node.js and are provided purely for
  // API completeness.
 
  composedPath() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kIsBeingDispatched] ? [this[kTarget]] : [];
  }
 
  get returnValue() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return !this.defaultPrevented;
  }
 
  get bubbles() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kBubbles];
  }
 
  get composed() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kComposed];
  }
 
  get eventPhase() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kIsBeingDispatched] ? Event.AT_TARGET : Event.NONE;
  }
 
  get cancelBubble() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    return this[kPropagationStopped];
  }
 
  set cancelBubble(value) {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    if (value) {
      this.stopPropagation();
    }
  }
 
  stopPropagation() {
    if (!isEvent(this))
      throw new ERR_INVALID_THIS('Event');
    this[kPropagationStopped] = true;
  }
 
  static NONE = 0;
  static CAPTURING_PHASE = 1;
  static AT_TARGET = 2;
  static BUBBLING_PHASE = 3;
}
 
const kEnumerableProperty = ObjectCreate(null);
kEnumerableProperty.enumerable = true;
 
ObjectDefineProperties(
  Event.prototype, {
    [SymbolToStringTag]: {
      writable: false,
      enumerable: false,
      configurable: true,
      value: 'Event',
    },
    stopImmediatePropagation: kEnumerableProperty,
    preventDefault: kEnumerableProperty,
    target: kEnumerableProperty,
    currentTarget: kEnumerableProperty,
    srcElement: kEnumerableProperty,
    type: kEnumerableProperty,
    cancelable: kEnumerableProperty,
    defaultPrevented: kEnumerableProperty,
    timeStamp: kEnumerableProperty,
    composedPath: kEnumerableProperty,
    returnValue: kEnumerableProperty,
    bubbles: kEnumerableProperty,
    composed: kEnumerableProperty,
    eventPhase: kEnumerableProperty,
    cancelBubble: kEnumerableProperty,
    stopPropagation: kEnumerableProperty,
  });
 
class NodeCustomEvent extends Event {
  constructor(type, options) {
    super(type, options);
    if (options?.detail) {
      this.detail = options.detail;
    }
  }
}
 
// Weak listener cleanup
// This has to be lazy for snapshots to work
let weakListenersState = null;
// The resource needs to retain the callback so that it doesn't
// get garbage collected now that it's weak.
let objectToWeakListenerMap = null;
function weakListeners() {
  weakListenersState ??= new SafeFinalizationRegistry(
    (listener) => listener.remove()
  );
  objectToWeakListenerMap ??= new SafeWeakMap();
  return { registry: weakListenersState, map: objectToWeakListenerMap };
}
 
// The listeners for an EventTarget are maintained as a linked list.
// Unfortunately, the way EventTarget is defined, listeners are accounted
// using the tuple [handler,capture], and even if we don't actually make
// use of capture or bubbling, in order to be spec compliant we have to
// take on the additional complexity of supporting it. Fortunately, using
// the linked list makes dispatching faster, even if adding/removing is
// slower.
class Listener {
  constructor(previous, listener, once, capture, passive,
              isNodeStyleListener, weak) {
    this.next = undefined;
    if (previous !== undefined)
      previous.next = this;
    this.previous = previous;
    this.listener = listener;
    // TODO(benjamingr) these 4 can be 'flags' to save 3 slots
    this.once = once;
    this.capture = capture;
    this.passive = passive;
    this.isNodeStyleListener = isNodeStyleListener;
    this.removed = false;
    this.weak = Boolean(weak); // Don't retain the object
 
    if (this.weak) {
      this.callback = new SafeWeakRef(listener);
      weakListeners().registry.register(listener, this, this);
      // Make the retainer retain the listener in a WeakMap
      weakListeners().map.set(weak, listener);
      this.listener = this.callback;
    } else if (typeof listener === 'function') {
      this.callback = listener;
      this.listener = listener;
    } else {
      this.callback = FunctionPrototypeBind(listener.handleEvent, listener);
      this.listener = listener;
    }
  }
 
  same(listener, capture) {
    const myListener = this.weak ? this.listener.deref() : this.listener;
    return myListener === listener && this.capture === capture;
  }
 
  remove() {
    if (this.previous !== undefined)
      this.previous.next = this.next;
    if (this.next !== undefined)
      this.next.previous = this.previous;
    this.removed = true;
    if (this.weak)
      weakListeners().registry.unregister(this);
  }
}
 
function initEventTarget(self) {
  self[kEvents] = new SafeMap();
  self[kMaxEventTargetListeners] = EventEmitter.defaultMaxListeners;
  self[kMaxEventTargetListenersWarned] = false;
}
 
class EventTarget {
  // Used in checking whether an object is an EventTarget. This is a well-known
  // symbol as EventTarget may be used cross-realm.
  // Ref: https://github.com/nodejs/node/pull/33661
  static [kIsEventTarget] = true;
 
  constructor() {
    initEventTarget(this);
  }
 
  [kNewListener](size, type, listener, once, capture, passive) {
    if (this[kMaxEventTargetListeners] > 0 &&
        size > this[kMaxEventTargetListeners] &&
        !this[kMaxEventTargetListenersWarned]) {
      this[kMaxEventTargetListenersWarned] = true;
      // No error code for this since it is a Warning
      // eslint-disable-next-line no-restricted-syntax
      const w = new Error('Possible EventTarget memory leak detected. ' +
                          `${size} ${type} listeners ` +
                          `added to ${inspect(this, { depth: -1 })}. Use ` +
                          'events.setMaxListeners() to increase limit');
      w.name = 'MaxListenersExceededWarning';
      w.target = this;
      w.type = type;
      w.count = size;
      process.emitWarning(w);
    }
  }
  [kRemoveListener](size, type, listener, capture) {}
 
  addEventListener(type, listener, options = {}) {
    if (!isEventTarget(this))
      throw new ERR_INVALID_THIS('EventTarget');
    if (arguments.length < 2)
      throw new ERR_MISSING_ARGS('type', 'listener');
 
    // We validateOptions before the shouldAddListeners check because the spec
    // requires us to hit getters.
    const {
      once,
      capture,
      passive,
      signal,
      isNodeStyleListener,
      weak,
    } = validateEventListenerOptions(options);
 
    if (!shouldAddListener(listener)) {
      // The DOM silently allows passing undefined as a second argument
      // No error code for this since it is a Warning
      // eslint-disable-next-line no-restricted-syntax
      const w = new Error(`addEventListener called with ${listener}` +
                          ' which has no effect.');
      w.name = 'AddEventListenerArgumentTypeWarning';
      w.target = this;
      w.type = type;
      process.emitWarning(w);
      return;
    }
    type = String(type);
 
    if (signal) {
      if (signal.aborted) {
        return;
      }
      // TODO(benjamingr) make this weak somehow? ideally the signal would
      // not prevent the event target from GC.
      signal.addEventListener('abort', () => {
        this.removeEventListener(type, listener, options);
      }, { once: true, [kWeakHandler]: this });
    }
 
    let root = this[kEvents].get(type);
 
    if (root === undefined) {
      root = { size: 1, next: undefined };
      // This is the first handler in our linked list.
      new Listener(root, listener, once, capture, passive,
                   isNodeStyleListener, weak);
      this[kNewListener](root.size, type, listener, once, capture, passive);
      this[kEvents].set(type, root);
      return;
    }
 
    let handler = root.next;
    let previous = root;
 
    // We have to walk the linked list to see if we have a match
    while (handler !== undefined && !handler.same(listener, capture)) {
      previous = handler;
      handler = handler.next;
    }
 
    if (handler !== undefined) { // Duplicate! Ignore
      return;
    }
 
    new Listener(previous, listener, once, capture, passive,
                 isNodeStyleListener, weak);
    root.size++;
    this[kNewListener](root.size, type, listener, once, capture, passive);
  }
 
  removeEventListener(type, listener, options = {}) {
    if (!isEventTarget(this))
      throw new ERR_INVALID_THIS('EventTarget');
    if (!shouldAddListener(listener))
      return;
 
    type = String(type);
    const capture = options?.capture === true;
 
    const root = this[kEvents].get(type);
    if (root === undefined || root.next === undefined)
      return;
 
    let handler = root.next;
    while (handler !== undefined) {
      if (handler.same(listener, capture)) {
        handler.remove();
        root.size--;
        if (root.size === 0)
          this[kEvents].delete(type);
        this[kRemoveListener](root.size, type, listener, capture);
        break;
      }
      handler = handler.next;
    }
  }
 
  dispatchEvent(event) {
    if (!isEventTarget(this))
      throw new ERR_INVALID_THIS('EventTarget');
 
    if (!(event instanceof Event))
      throw new ERR_INVALID_ARG_TYPE('event', 'Event', event);
 
    if (event[kIsBeingDispatched])
      throw new ERR_EVENT_RECURSION(event.type);
 
    this[kHybridDispatch](event, event.type, event);
 
    return event.defaultPrevented !== true;
  }
 
  [kHybridDispatch](nodeValue, type, event) {
    const createEvent = () => {
      if (event === undefined) {
        event = this[kCreateEvent](nodeValue, type);
        event[kTarget] = this;
        event[kIsBeingDispatched] = true;
      }
      return event;
    };
    if (event !== undefined) {
      event[kTarget] = this;
      event[kIsBeingDispatched] = true;
    }
 
    const root = this[kEvents].get(type);
    if (root === undefined || root.next === undefined)
      return true;
 
    let handler = root.next;
    let next;
 
    while (handler !== undefined &&
           (handler.passive || event?.[kStop] !== true)) {
      // Cache the next item in case this iteration removes the current one
      next = handler.next;
 
      if (handler.removed) {
        // Deal with the case an event is removed while event handlers are
        // Being processed (removeEventListener called from a listener)
        handler = next;
        continue;
      }
      if (handler.once) {
        handler.remove();
        root.size--;
        const { listener, capture } = handler;
        this[kRemoveListener](root.size, type, listener, capture);
      }
 
      try {
        let arg;
        if (handler.isNodeStyleListener) {
          arg = nodeValue;
        } else {
          arg = createEvent();
        }
        const callback = handler.weak ?
          handler.callback.deref() : handler.callback;
        let result;
        if (callback) {
          result = FunctionPrototypeCall(callback, this, arg);
          if (!handler.isNodeStyleListener) {
            arg[kIsBeingDispatched] = false;
          }
        }
        if (result !== undefined && result !== null)
          addCatch(result);
      } catch (err) {
        emitUncaughtException(err);
      }
 
      handler = next;
    }
 
    if (event !== undefined)
      event[kIsBeingDispatched] = false;
  }
 
  [kCreateEvent](nodeValue, type) {
    return new NodeCustomEvent(type, { detail: nodeValue });
  }
  [customInspectSymbol](depth, options) {
    if (!isEventTarget(this))
      throw new ERR_INVALID_THIS('EventTarget');
    const name = this.constructor.name;
    if (depth < 0)
      return name;
 
    const opts = ObjectAssign({}, options, {
      depth: NumberIsInteger(options.depth) ? options.depth - 1 : options.depth
    });
 
    return `${name} ${inspect({}, opts)}`;
  }
}
 
ObjectDefineProperties(EventTarget.prototype, {
  addEventListener: kEnumerableProperty,
  removeEventListener: kEnumerableProperty,
  dispatchEvent: kEnumerableProperty,
  [SymbolToStringTag]: {
    writable: false,
    enumerable: false,
    configurable: true,
    value: 'EventTarget',
  }
});
 
function initNodeEventTarget(self) {
  initEventTarget(self);
}
 
class NodeEventTarget extends EventTarget {
  static [kIsNodeEventTarget] = true;
  static defaultMaxListeners = 10;
 
  constructor() {
    super();
    initNodeEventTarget(this);
  }
 
  setMaxListeners(n) {
    if (!isNodeEventTarget(this))
      throw new ERR_INVALID_THIS('NodeEventTarget');
    EventEmitter.setMaxListeners(n, this);
  }
 
  getMaxListeners() {
    if (!isNodeEventTarget(this))
      throw new ERR_INVALID_THIS('NodeEventTarget');
    return this[kMaxEventTargetListeners];
  }
 
  eventNames() {
    if (!isNodeEventTarget(this))
      throw new ERR_INVALID_THIS('NodeEventTarget');
    return ArrayFrom(this[kEvents].keys());
  }
 
  listenerCount(type) {
    if (!isNodeEventTarget(this))
      throw new ERR_INVALID_THIS('NodeEventTarget');
    const root = this[kEvents].get(String(type));
    return root !== undefined ? root.size : 0;
  }
 
  off(type, listener, options) {
    if (!isNodeEventTarget(this))
      throw new ERR_INVALID_THIS('NodeEventTarget');
    this.removeEventListener(type, listener, options);
    return this;
  }
 
  removeListener(type, listener, options) {
    if (!isNodeEventTarget(this))
      throw new ERR_INVALID_THIS('NodeEventTarget');
    this.removeEventListener(type, listener, options);
    return this;
  }
 
  on(type, listener) {
    if (!isNodeEventTarget(this))
      throw new ERR_INVALID_THIS('NodeEventTarget');
    this.addEventListener(type, listener, { [kIsNodeStyleListener]: true });
    return this;
  }
 
  addListener(type, listener) {
    if (!isNodeEventTarget(this))
      throw new ERR_INVALID_THIS('NodeEventTarget');
    this.addEventListener(type, listener, { [kIsNodeStyleListener]: true });
    return this;
  }
  emit(type, arg) {
    if (!isNodeEventTarget(this))
      throw new ERR_INVALID_THIS('NodeEventTarget');
    validateString(type, 'type');
    const hadListeners = this.listenerCount(type) > 0;
    this[kHybridDispatch](arg, type);
    return hadListeners;
  }
 
  once(type, listener) {
    if (!isNodeEventTarget(this))
      throw new ERR_INVALID_THIS('NodeEventTarget');
    this.addEventListener(type, listener,
                          { once: true, [kIsNodeStyleListener]: true });
    return this;
  }
 
  removeAllListeners(type) {
    if (!isNodeEventTarget(this))
      throw new ERR_INVALID_THIS('NodeEventTarget');
    if (type !== undefined) {
      this[kEvents].delete(String(type));
    } else {
      this[kEvents].clear();
    }
 
    return this;
  }
}
 
ObjectDefineProperties(NodeEventTarget.prototype, {
  setMaxListeners: kEnumerableProperty,
  getMaxListeners: kEnumerableProperty,
  eventNames: kEnumerableProperty,
  listenerCount: kEnumerableProperty,
  off: kEnumerableProperty,
  removeListener: kEnumerableProperty,
  on: kEnumerableProperty,
  addListener: kEnumerableProperty,
  once: kEnumerableProperty,
  emit: kEnumerableProperty,
  removeAllListeners: kEnumerableProperty,
});
 
// EventTarget API
 
function shouldAddListener(listener) {
  if (typeof listener === 'function' ||
      typeof listener?.handleEvent === 'function') {
    return true;
  }
 
  if (listener == null)
    return false;
 
  throw new ERR_INVALID_ARG_TYPE('listener', 'EventListener', listener);
}
 
function validateEventListenerOptions(options) {
  if (typeof options === 'boolean')
    return { capture: options };
 
  if (options === null)
    return {};
  validateObject(options, 'options', {
    allowArray: true, allowFunction: true,
  });
  return {
    once: Boolean(options.once),
    capture: Boolean(options.capture),
    passive: Boolean(options.passive),
    signal: options.signal,
    weak: options[kWeakHandler],
    isNodeStyleListener: Boolean(options[kIsNodeStyleListener])
  };
}
 
// Test whether the argument is an event object. This is far from a fool-proof
// test, for example this input will result in a false positive:
// > isEventTarget({ constructor: EventTarget })
// It stands in its current implementation as a compromise.
// Ref: https://github.com/nodejs/node/pull/33661
function isEventTarget(obj) {
  return obj?.constructor?.[kIsEventTarget];
}
 
function isNodeEventTarget(obj) {
  return obj?.constructor?.[kIsNodeEventTarget];
}
 
function addCatch(promise) {
  const then = promise.then;
  if (typeof then === 'function') {
    FunctionPrototypeCall(then, promise, undefined, function(err) {
      // The callback is called with nextTick to avoid a follow-up
      // rejection from this promise.
      emitUncaughtException(err);
    });
  }
}
 
function emitUncaughtException(err) {
  process.nextTick(() => { throw err; });
}
 
function makeEventHandler(handler) {
  // Event handlers are dispatched in the order they were first set
  // See https://github.com/nodejs/node/pull/35949#issuecomment-722496598
  function eventHandler(...args) {
    if (typeof eventHandler.handler !== 'function') {
      return;
    }
    return ReflectApply(eventHandler.handler, this, args);
  }
  eventHandler.handler = handler;
  return eventHandler;
}
 
function defineEventHandler(emitter, name) {
  // 8.1.5.1 Event handlers - basically `on[eventName]` attributes
  ObjectDefineProperty(emitter, `on${name}`, {
    get() {
      return this[kHandlers]?.get(name)?.handler;
    },
    set(value) {
      if (!this[kHandlers]) {
        this[kHandlers] = new SafeMap();
      }
      let wrappedHandler = this[kHandlers]?.get(name);
      if (wrappedHandler) {
        if (typeof wrappedHandler.handler === 'function') {
          this[kEvents].get(name).size--;
          const size = this[kEvents].get(name).size;
          this[kRemoveListener](size, name, wrappedHandler.handler, false);
        }
        wrappedHandler.handler = value;
        if (typeof wrappedHandler.handler === 'function') {
          this[kEvents].get(name).size++;
          const size = this[kEvents].get(name).size;
          this[kNewListener](size, name, value, false, false, false);
        }
      } else {
        wrappedHandler = makeEventHandler(value);
        this.addEventListener(name, wrappedHandler);
      }
      this[kHandlers].set(name, wrappedHandler);
    },
    configurable: true,
    enumerable: true
  });
}
 
const EventEmitterMixin = (Superclass) => {
  class MixedEventEmitter extends Superclass {
    constructor(...args) {
      args = new SafeArrayIterator(args);
      super(...args);
      FunctionPrototypeCall(EventEmitter, this);
    }
  }
  const protoProps = ObjectGetOwnPropertyDescriptors(EventEmitter.prototype);
  delete protoProps.constructor;
  ObjectDefineProperties(MixedEventEmitter.prototype, protoProps);
  return MixedEventEmitter;
};
 
module.exports = {
  Event,
  EventEmitterMixin,
  EventTarget,
  NodeEventTarget,
  defineEventHandler,
  initEventTarget,
  initNodeEventTarget,
  kCreateEvent,
  kNewListener,
  kTrustEvent,
  kRemoveListener,
  kEvents,
  kWeakHandler,
  isEventTarget,
};