code: function (id) {
  		var container = this._container = L.DomUtil.get(id);
  
  		if (!container) {
  			throw new Error('Map container not found.');
  		} else if (container._leaflet) {
  			throw new Error('Map container is already initialized.');
  		}
  
  		container._leaflet = true;
  	}
docs: map initialization methods