对象属性返回未定义的，即使它存在JavaScript。

Question

我试着用对象制作口袋妖怪的克隆系统。使用PokeAPI，我可以得到所有口袋妖怪的进化过程，如果口袋妖怪有一个以上的进化，(即Kirlia)，它会推送所有的进化对象属性-- Pokemon.evolutions，这是这些进化对象的数组。当我试图编译代码时，它会崩溃，上面写着：TypeError: Cannot read properties of undefined (reading 'species')，所以我认为它意味着，因为我输入了对象，但不是这样，如果我console.log data.evolves_to[i].species.name (导致应用程序崩溃的行)，我会得到口袋妖怪的名字，它是正确的！然后它在同一条线上坠毁！它被登录到控制台，然后崩溃。到底怎么回事？以下是上下文代码：

 async getRandomPokemon() {
    const rawData: PokemonData[] | PokemonSpecies[] = [];
    const id = utils.rng({ min: 1, max: 898 });
    rawData[0] = await api.getPokemonById(id);
    rawData[1] = await api.getPokemonSpeciesById(id);
    const pokemon: Pokemon = {
      name: rawData[0].name,
      level: utils.rng({ min: 1, max: 10 }),
      gender: utils.pick({ array: ["male", "female"] }),
      exp: 1,
      stats: {
        hp: rawData[0].stats[0].base_stat,
        atk: rawData[0].stats[1].base_stat,
        def: rawData[0].stats[2].base_stat,
        spa: rawData[0].stats[3].base_stat,
        spd: rawData[0].stats[4].base_stat,
        spe: rawData[0].stats[5].base_stat,
        IVs: {
          hp: utils.rng({ min: 0, max: 31 }),
          atk: utils.rng({ min: 0, max: 31 }),
          def: utils.rng({ min: 0, max: 31 }),
          spa: utils.rng({ min: 0, max: 31 }),
          spd: utils.rng({ min: 0, max: 31 }),
          spe: utils.rng({ min: 0, max: 31 }),
        },
        EVs: {
          hp: utils.rng({ min: 0, max: 252 }),
          atk: utils.rng({ min: 0, max: 252 }),
          def: utils.rng({ min: 0, max: 252 }),
          spa: utils.rng({ min: 0, max: 252 }),
          spd: utils.rng({ min: 0, max: 252 }),
          spe: utils.rng({ min: 0, max: 252 }),
        },
      },
      moves: [],
      evolutions: [],
      aesthetics: {
        sprite: rawData[0].sprites.front_default,
        color: rawData[1].color.name,
      },
      rarity: {
        isLegendary: rawData[1].is_legendary,
        isMythical: rawData[1].is_mythical,
        catchRate: rawData[1].capture_rate,
      },
    };
    const json = await axios(rawData[1].evolution_chain.url);
    let data = json.data.chain;
    for (let i = 0; i < data.evolves_to.length; i++) {
      const one: boolean = data.evolves_to[i].evolves_to.length === 0;
      pokemon.evolutions.push({
        first: data.species.name,
        second: {
          name: data.evolves_to[i].species.name,
          mode: {
            name: data.evolves_to[i].evolution_details[0].trigger.name,
            gender: data.evolves_to[i].evolution_details[0].gender,
            level: data.evolves_to[i].evolution_details[0].min_level,
            item: data.evolves_to[i].evolution_details[0].item
              ? data.evolves_to[i].evolution_details[0].item.name
              : null,
            happiness: data.evolves_to[i].evolution_details[0].min_happiness,
            move: data.evolves_to[i].evolution_details[0].known_move,
          },
        },
        third: one
          ? null
          : {
              name: one ? null : data.evolves_to[i].evolves_to[0].species.name,
              mode: {
                name: data.evolves_to[i].evolves_to[0].evolution_details[0]
                  .trigger.name,
                gender:
                  data.evolves_to[i].evolves_to[0].evolution_details[0].gender,
                level:
                  data.evolves_to[i].evolves_to[0].evolution_details[0]
                    .min_level,
                item: data.evolves_to[i].evolves_to[0].evolution_details[0].item
                  ? data.evolves_to[i].evolves_to[0].evolution_details[0].item
                      .name
                  : null,
                happiness:
                  data.evolves_to[i].evolves_to[0].evolution_details[0]
                    .min_happiness,
                move: data.evolves_to[i].evolves_to[0].evolution_details[0]
                  .known_move,
              },
            },
      });
      if (data.evolves_to[0].evolves_to.length > 1) {
        for (let i = 0; i < data.evolves_to[0].evolves_to.length; i++) {
          console.log(data.evolves_to[i].species.name);
          pokemon.evolutions.push({
            first: data.species.name,
            second: {
              name: data.evolves_to[i].species.name,
              mode: {
                name: data.evolves_to[i].evolution_details[0].trigger.name,
                gender: data.evolves_to[i].evolution_details[0].gender,
                level: data.evolves_to[i].evolution_details[0].min_level,
                item: data.evolves_to[i].evolution_details[0].item
                  ? data.evolves_to[i].evolution_details[0].item.name
                  : null,
                happiness:
                  data.evolves_to[i].evolution_details[0].min_happiness,
                move: data.evolves_to[i].evolution_details[0].known_move,
              },
            },
            third: one
              ? null
              : {
                  name: one
                    ? null
                    : data.evolves_to[i].evolves_to[0].species.name,
                  mode: {
                    name: data.evolves_to[i].evolves_to[0].evolution_details[0]
                      .trigger.name,
                    gender:
                      data.evolves_to[i].evolves_to[0].evolution_details[0]
                        .gender,
                    level:
                      data.evolves_to[i].evolves_to[0].evolution_details[0]
                        .min_level,
                    item: data.evolves_to[i].evolves_to[0].evolution_details[0]
                      .item
                      ? data.evolves_to[i].evolves_to[0].evolution_details[0]
                          .item.name
                      : null,
                    happiness:
                      data.evolves_to[i].evolves_to[0].evolution_details[0]
                        .min_happiness,
                    move: data.evolves_to[i].evolves_to[0].evolution_details[0]
                      .known_move,
                  },
                },
          });
        }
      }
    }
    return pokemon;
  },

应用程序崩溃的代码是console.log(data.evolves_to[i].species.name); (106，几乎位于底部)。奇怪的是，当获得第一次进化时，data.evolves_to[i].species.name已经在使用，但是当试图获得替代的进化时会崩溃。

Answer 1

for循环就在您的console.log之上导致了这个问题。

for (let i = 0; i < data.evolves_to[0].evolves_to.length; i++)

当我认为你只需要"data.evolves_to.evolves_to.length“的时候，你就有了"data.evolves_to.length”。

如果"data.evolves_to“中的对象比"data.evolves_to.evolves_to”中的对象少，那么这种情况就会发生。

您可以尝试通过使用浏览器开发控制台逐步遍历程序来查找错误。

这显然是一个复制和粘贴错误，现在我们知道要寻找什么。