code: function () {
      // Create hash table for easy reference
      var collectionValues = hashTable(this.collection.toJSON(), 'label', 'value')
      var filteredCollectionValues = hashTable(this.filteredCollection.toJSON(), 'label', 'value')
  
      // Add value from hash tables to geojson properties
      var idAttribute = this.boundaries.idAttribute
      var filtered = this.filteredCollection.getFilters().length
      this.boundaries.forEach(function (item) {
        var properties = item.get('properties')
        properties.value = collectionValues[properties[idAttribute]]
        if (filtered) {
          properties.filteredValue = filteredCollectionValues[properties[idAttribute]] || 0
        }
        item.set('properties', properties)
      }, this)
    }
docs: Loop through features, find the matching dataset record, and put the specific field into the feature
  Done via reference