document.addEventListener("DOMContentLoaded", function(event) {
        console.log("document loaded");
      });

marker.addListener("click", () => {
      this.reserveButton = document.getElementById("reserve");
      this.reserveButton.addEventListener("click", this.reserveFunction);
}

openReserveModal: (order, vendor) => dispatch(openModal({ type: 'reserve', order: order, vendor: vendor }))

this.MarkerManager = new MarkerManager(
      this.map,
      this.props.openReserveModal
    );

constructor(map, modal) {
    this.map = map;
    this.modal = modal;
    this.markers = {};
    this.openWindow = null;
    this.highlight = null;
    this.reserveButton = null;
    this.reserveFunction = null;

<div id="map-reserve" class="info-win-name info-win-reserve">
 RESERVE
</div >

this.reserveFunction = () => {
        this.modal(order, vendor);
      };