react-beautiful-dnd/src/state/get-displacement-map.js

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

// @flow
import memoizeOne from 'memoize-one';
import type { DraggableId, Displacement } from '../types';

export type DisplacementMap = { [key: DraggableId]: Displacement };

// shared map creation
// it saves needing to loop over the list in every component
// a really important optimisation for big lists
export default memoizeOne(
  (displaced: Displacement[]): DisplacementMap =>
    displaced.reduce((map: DisplacementMap, displacement: Displacement) => {
      map[displacement.draggableId] = displacement;
      return map;
    }, {}),
);