text: const OpenToMapLayer = L.TileLayer.extend({
      initialize: function(url, options) {
          this._url = url;
          L.setOptions(this, options);
      }
  });
  
  let instance = null;
  
  class openToMapLayer {
      constructor(url ,options){
          if (instance) {
              return instance
          }
          this.name = 'Open To Map Layer';
          this.id = 'openToMapLayer';
          this._url = url || 'http://{s}.tile.opentopomap.org/{z}/{x}/{y}.png';
  
  
          this.options = Object.assign({}, options, this.options);
          instance = this;
      }
  
      Layer(url ,options){
          let _url = url || this._url;
          let _options = Object.assign({}, options, this.options);
          return new OpenToMapLayer(_url , _options);
      }
  
      /*static layer(url ,options){
          let _url = url || 'http://{s}.tile.opentopomap.org/{z}/{x}/{y}.png';
          return new L.TileLayer(_url ,options);
      }*/
  }
  
  export default openToMapLayer;