Function defineEventHandler

lib/internal/event_target.js:1134–1179

(emitter, name, event = name)

}

function defineEventHandler(emitter, name, event = name) {
  // 8.1.5.1 Event handlers - basically `on[eventName]` attributes
  const propName = `on${name}`;
  function get() {
    validateThisInternalField(this, kHandlers, 'EventTarget');
    return this[kHandlers]?.get(event)?.handler ?? null;
  }
  ObjectDefineProperty(get, 'name', {
    __proto__: null,
    value: `get ${propName}`,
  });

  function set(value) {
    validateThisInternalField(this, kHandlers, 'EventTarget');
    let wrappedHandler = this[kHandlers]?.get(event);
    if (wrappedHandler) {
      if (typeof wrappedHandler.handler === 'function') {
        this[kEvents].get(event).size--;
        const size = this[kEvents].get(event).size;
        this[kRemoveListener](size, event, wrappedHandler.handler, false);
      }
      wrappedHandler.handler = value;
      if (typeof wrappedHandler.handler === 'function') {
        this[kEvents].get(event).size++;
        const size = this[kEvents].get(event).size;
        this[kNewListener](size, event, value, false, false, false, false);
      }
    } else {
      wrappedHandler = makeEventHandler(value);
      this.addEventListener(event, wrappedHandler);
    }
    this[kHandlers].set(event, wrappedHandler);
  }
  ObjectDefineProperty(set, 'name', {
    __proto__: null,
    value: `set ${propName}`,
  });

  ObjectDefineProperty(emitter, propName, {
    __proto__: null,
    get,
    set,
    configurable: true,
    enumerable: true,
  });
}

module.exports = {
  Event,