hasEventListener( type, listener ) {

		const listeners = this._listeners;

		if ( listeners === undefined ) return false;

		return listeners[ type ] !== undefined && listeners[ type ].indexOf( listener ) !== -1;

	}
Returns `true` if the given event listener has been added to the given event type.

@param {string} type - The type of event.
@param {Function} listener - The listener to check.
@return {boolean} Whether the given event listener has been added to the given event type.