react-beautiful-dnd/src/state/get-draggables-inside-droppable.js

Beautiful, accessible drag and drop for lists with React.js

// @flow
import memoizeOne from 'memoize-one';
import { toDraggableList } from './dimension-structures';
import type {
  DraggableDimension,
  DroppableDimension,
  DraggableDimensionMap,
} from '../types';

export default memoizeOne(
  (
    droppable: DroppableDimension,
    draggables: DraggableDimensionMap,
  ): DraggableDimension[] =>
    toDraggableList(draggables)
      .filter(
        (draggable: DraggableDimension): boolean =>
          droppable.descriptor.id === draggable.descriptor.droppableId,
      )
      // Dimensions are not guarenteed to be ordered in the same order as keys
      // So we need to sort them so they are in the correct order
      .sort(
        (a: DraggableDimension, b: DraggableDimension): number =>
          a.descriptor.index - b.descriptor.index,
      ),
);