react-beautiful-dnd/src/state/with-droppable-scroll.js

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

// @flow
import { type Position } from 'css-box-model';
import { add } from './position';
import type { Scrollable, DroppableDimension } from '../types';

export default (droppable: DroppableDimension, point: Position): Position => {
  const closestScrollable: ?Scrollable = droppable.viewport.closestScrollable;
  if (!closestScrollable) {
    return point;
  }

  return add(point, closestScrollable.scroll.diff.value);
};