showOverlay

shows the overlay message over the body of DataGrid

function showOverlay(
    // the text or the html string that will be shown as the overlay message
    message: string
): void

webix.grid({
  on:{
    onBeforeLoad:function(){
      this.showOverlay("Loading...");
    }
  }
});

also check the next samples:

Good for “Loading” and “No data” notifications.

Can be styled with the help of the webix_datatable_overlay css class.