Skeleton for implementing a custom overlay for google maps.

overlay.js

class CustomOverlay {
  constructor() {
    this.overlay = new google.maps.OverlayView();
    this.overlay.onAdd = () => this.onAdd();
    this.overlay.onRemove = () => this.onRemove();
    this.overlay.draw = () => this.draw();
  }
  onAdd() { /* ... */ }
  onRemove() { /* ... */ }
  draw() {
    const p = this.overlay.getProjection();
    const pane = this.overlay.getPanes().floatPane;

    // [...]
  }

  setMap(map) { this.overlay.setMap(map); }
  getMap() { return this.overlay.getMap(); }
}


// ... somewhere else (when api is loaded):
const map = new google.maps.Map( /* ... */ );
const overlay = new CustomOverlay();
overlay.setMap(map);