node_modules/zone.js/lib/browser/event-target.ts

/**
 * @license
 * Copyright Google Inc. All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

export function eventTargetPatch(_global: any, api: _ZonePrivate) {
  if ((Zone as any)[api.symbol('patchEventTarget')]) {
    // EventTarget is already patched.
    return;
  }
  const {eventNames, zoneSymbolEventNames, TRUE_STR, FALSE_STR, ZONE_SYMBOL_PREFIX} =
      api.getGlobalObjects()!;
  //  predefine all __zone_symbol__ + eventName + true/false string
  for (let i = 0; i < eventNames.length; i++) {
    const eventName = eventNames[i];
    const falseEventName = eventName + FALSE_STR;
    const trueEventName = eventName + TRUE_STR;
    const symbol = ZONE_SYMBOL_PREFIX + falseEventName;
    const symbolCapture = ZONE_SYMBOL_PREFIX + trueEventName;
    zoneSymbolEventNames[eventName] = {};
    zoneSymbolEventNames[eventName][FALSE_STR] = symbol;
    zoneSymbolEventNames[eventName][TRUE_STR] = symbolCapture;
  }

  const EVENT_TARGET = _global['EventTarget'];
  if (!EVENT_TARGET || !EVENT_TARGET.prototype) {
    return;
  }
  api.patchEventTarget(_global, [EVENT_TARGET && EVENT_TARGET.prototype]);

  return true;
}

export function patchEvent(global: any, api: _ZonePrivate) {
  api.patchEventPrototype(global, api);
}