REACT选择状态结构（3）

import { useState } from 'react';
import { initialTravelPlan } from './places.js';
 
export default function TravelPlan() {
  const [plan, setPlan] = useState(initialTravelPlan);
 
  function handleComplete(parentId, childId) {
    const parent = plan[parentId];
    // Create a new version of the parent place
    // that doesn't include this child ID.
    const nextParent = {
      ...parent,
      childIds: parent.childIds
        .filter(id => id !== childId)
    };
    // Update the root state object...
    setPlan({
      ...plan,
      // ...so that it has the updated parent.
      [parentId]: nextParent
    });
  }
 
  const root = plan[0];
  const planetIds = root.childIds;
  return (
    <>
      <h2>Places to visit</h2>
      <ol>
        {planetIds.map(id => (
          <PlaceTree
            key={id}
            id={id}
            parentId={0}
            placesById={plan}
            onComplete={handleComplete}
          />
        ))}
      </ol>
    </>
  );
}
 
function PlaceTree({ id, parentId, placesById, onComplete }) {
  const place = placesById[id];
  const childIds = place.childIds;
  return (
    <li>
      {place.title}
      <button onClick={() => {
        onComplete(parentId, id);
      }}>
        Complete
      </button>
      {childIds.length > 0 &&
        <ol>
          {childIds.map(childId => (
            <PlaceTree
              key={childId}
              id={childId}
              parentId={id}
              placesById={placesById}
              onComplete={onComplete}
            />
          ))}
        </ol>
      }
    </li>
  );
}

export const initialTravelPlan = {
  0: {
    id: 0,
    title: '(Root)',
    childIds: [1, 42, 46],
  },
  1: {
    id: 1,
    title: 'Earth',
    childIds: [2, 10, 19, 26, 34]
  },
  2: {
    id: 2,
    title: 'Africa',
    childIds: [3, 4, 5, 6 , 7, 8, 9]
  }, 
  3: {
    id: 3,
    title: 'Botswana',
    childIds: []
  },
  4: {
    id: 4,
    title: 'Egypt',
    childIds: []
  },
  5: {
    id: 5,
    title: 'Kenya',
    childIds: []
  },
  6: {
    id: 6,
    title: 'Madagascar',
    childIds: []
  }, 
  7: {
    id: 7,
    title: 'Morocco',
    childIds: []
  },
  8: {
    id: 8,
    title: 'Nigeria',
    childIds: []
  },
  9: {
    id: 9,
    title: 'South Africa',
    childIds: []
  },
  10: {
    id: 10,
    title: 'Americas',
    childIds: [11, 12, 13, 14, 15, 16, 17, 18],   
  },
  11: {
    id: 11,
    title: 'Argentina',
    childIds: []
  },
  12: {
    id: 12,
    title: 'Brazil',
    childIds: []
  },
  13: {
    id: 13,
    title: 'Barbados',
    childIds: []
  }, 
  14: {
    id: 14,
    title: 'Canada',
    childIds: []
  },
  15: {
    id: 15,
    title: 'Jamaica',
    childIds: []
  },
  16: {
    id: 16,
    title: 'Mexico',
    childIds: []
  },
  17: {
    id: 17,
    title: 'Trinidad and Tobago',
    childIds: []
  },
  18: {
    id: 18,
    title: 'Venezuela',
    childIds: []
  },
  19: {
    id: 19,
    title: 'Asia',
    childIds: [20, 21, 22, 23, 24, 25],   
  },
  20: {
    id: 20,
    title: 'China',
    childIds: []
  },
  21: {
    id: 21,
    title: 'India',
    childIds: []
  },
  22: {
    id: 22,
    title: 'Singapore',
    childIds: []
  },
  23: {
    id: 23,
    title: 'South Korea',
    childIds: []
  },
  24: {
    id: 24,
    title: 'Thailand',
    childIds: []
  },
  25: {
    id: 25,
    title: 'Vietnam',
    childIds: []
  },
  26: {
    id: 26,
    title: 'Europe',
    childIds: [27, 28, 29, 30, 31, 32, 33],   
  },
  27: {
    id: 27,
    title: 'Croatia',
    childIds: []
  },
  28: {
    id: 28,
    title: 'France',
    childIds: []
  },
  29: {
    id: 29,
    title: 'Germany',
    childIds: []
  },
  30: {
    id: 30,
    title: 'Italy',
    childIds: []
  },
  31: {
    id: 31,
    title: 'Portugal',
    childIds: []
  },
  32: {
    id: 32,
    title: 'Spain',
    childIds: []
  },
  33: {
    id: 33,
    title: 'Turkey',
    childIds: []
  },
  34: {
    id: 34,
    title: 'Oceania',
    childIds: [35, 36, 37, 38, 39, 40, 41],   
  },
  35: {
    id: 35,
    title: 'Australia',
    childIds: []
  },
  36: {
    id: 36,
    title: 'Bora Bora (French Polynesia)',
    childIds: []
  },
  37: {
    id: 37,
    title: 'Easter Island (Chile)',
    childIds: []
  },
  38: {
    id: 38,
    title: 'Fiji',
    childIds: []
  },
  39: {
    id: 39,
    title: 'Hawaii (the USA)',
    childIds: []
  },
  40: {
    id: 40,
    title: 'New Zealand',
    childIds: []
  },
  41: {
    id: 41,
    title: 'Vanuatu',
    childIds: []
  },
  42: {
    id: 42,
    title: 'Moon',
    childIds: [43, 44, 45]
  },
  43: {
    id: 43,
    title: 'Rheita',
    childIds: []
  },
  44: {
    id: 44,
    title: 'Piccolomini',
    childIds: []
  },
  45: {
    id: 45,
    title: 'Tycho',
    childIds: []
  },
  46: {
    id: 46,
    title: 'Mars',
    childIds: [47, 48]
  },
  47: {
    id: 47,
    title: 'Corn Town',
    childIds: []
  },
  48: {
    id: 48,
    title: 'Green Hill',
    childIds: []
  }
};