setState in multiple fetch requests(多个获取请求中的 setState)

问题描述

我正在为求职面试做 StarWars API 任务.

我的代码看起来像这样，我不知道 setCharacters 钩子应该在什么位置.首先呈现页面，然后设置状态.我需要在所有提取完成后呈现页面.

为了提高效率，我将之前的提取更改为 Promise.all() 但现在我被 setCharacters 放置所困.之前的话题可以看这里

I'am doing the StarWars API task for the job interview.

my code look like that and I don't know in what place the setCharacters hook should be. First the page is rendered and then the state is set. I need the page to be rendered when all the fetches are done.

To try to be more efficient i changed the previous fetches into Promise.all() but right now I'am stuck with the setCharacters placement. The previous topic can be seen here useEffect efficiency in Star Wars API

const api = `https://swapi.dev/api/people/`;
    const [characters, setCharacters] = useState([]);
    const [fetched, setFetched] = useState(false);

    useEffect(() => {
        const fetchOtherData = (characters) => {
            const charactersWithAllData = [];
            characters.forEach((character) => {
                const homeworld = character.homeworld;
                const species = character.species;
                const vehicles = character.vehicles;
                const starships = character.starships;
                let urls = [homeworld, ...species, ...vehicles, ...starships];

                Promise.all(
                    urls.map((url) => {
                        if (url.length) {
                            fetch(url)
                                .then((response) => response.json())
                                .then((data) => {
                                    if (url.search("species") > 0) {
                                        character.species = data.name;
                                    }
                                    if (url.search("planets") > 0) {
                                        character.homeworld = data.name;
                                    }
                                    if (url.search("vehicles") > 0) {
                                        character.vehicles.shift();
                                        character.vehicles.push(data.name);
                                    }
                                    if (url.search("starships") > 0) {
                                        character.starships.shift();
                                        character.starships.push(data.name);
                                    }
                                })
                                .catch((err) => console.error(err));
                        }
                        if (!url.length) {
                            if (url.search("species")) {
                                character.species = "Unspecified";
                            }
                            if (url.search("vehicles")) {
                                character.vehicles = "";
                            }
                            if (url.search("starships")) {
                                character.starships = "";
                            }
                        }
                    })
                ).then(charactersWithAllData.push(character));
            });
            setCharacters(charactersWithAllData);
        };

        const fetchApi = () => {
            const characters = [];
            Promise.all(
                [api].map((api) =>
                    fetch(api)
                        .then((response) => response.json())
                        .then((data) => characters.push(...data.results))
                        .then((data) => fetchOtherData(characters))
                        .then(setFetched(true))
                )
            );
        };
        fetchApi();
    }, []);

Thanks for all the of the possible replies.

Issue

Found a few issues:

1. Primary Issue: The fetchApi function's Promise.all chain was immediately invoking setFetched(true) instead of waiting for the chain's thenable to invoke it. This is why you are seeing the empty table before the data has been fetched and processed.

   const fetchApi = () => {
     const characters = [];
     Promise.all(
       [api].map((api) =>
         fetch(api)
           .then((response) => response.json())
           .then((data) => characters.push(...data.results))
           .then((data) => fetchOtherData(characters))
           .then(setFetched(true)) // <-- immediately invoked
       )
     );
   };
   

2. fetchOtherData function is also synchronous and doesn't return a Promise so the outer Promise-chain in fetchApi doesn't wait for the processing to complete, this is why you still see URL strings instead of the resolved values from the fetch.

Solution

Fix the Promise chain in fetchApi to be invoked in the .then callback. Rework the logic in fetchOtherData to wait for the additional fetch requests to resolve.

Here's my suggested solution:

const api = `https://swapi.dev/api/people/`;

function App() {
  const basicClassName = "starWarsApi";
  const [characters, setCharacters] = useState([]);
  const [fetched, setFetched] = useState(false);

  useEffect(() => {
    const fetchOtherData = async (characters) => {
      const characterReqs = characters.map(async (character) => {
        const { homeworld, species, starships, vehicles } = character;
        const urls = [homeworld, ...species, ...vehicles, ...starships];

        // Make shallow copy to mutate
        const characterWithAllData = { ...character };

        const urlReqs = urls.map(async (url) => {
          if (url.length) {
            try {
              const response = await fetch(url);
              const { name } = await response.json();
              if (url.includes("species")) {
                characterWithAllData.species = name;
              }
              if (url.includes("planets")) {
                characterWithAllData.homeworld = name;
              }
              if (url.includes("vehicles")) {
                characterWithAllData.vehicles.shift();
                characterWithAllData.vehicles.push(name);
              }
              if (url.includes("starships")) {
                characterWithAllData.starships.shift();
                characterWithAllData.starships.push(name);
              }
            } catch (err) {
              console.error(err);
            }
          } else {
            if (url.includes("species")) {
              characterWithAllData.species = "Unspecified";
            }
            if (url.includes("vehicles")) {
              characterWithAllData.vehicles = "";
            }
            if (url.includes("starships")) {
              characterWithAllData.starships = "";
            }
          }
        });

        await Promise.all(urlReqs); // <-- wait for mutations/updates
        return characterWithAllData;
      });

      return Promise.all(characterReqs);
    };

    const fetchApi = () => {
      Promise.all(
        [api].map((api) =>
          fetch(api)
            .then((response) => response.json())
            .then((data) => fetchOtherData(data.results))
            .then((charactersWithAllData) => {
              setCharacters(charactersWithAllData);
              setFetched(true);
            })
        )
      );
    };
    fetchApi();
  }, []);

  return (
    <div className={basicClassName}>
      {fetched && (
        <>
          <h1 className={`${basicClassName}__heading`}>Characters</h1>
          <div className={`${basicClassName}__inputsAndBtnsSection`}>
            <FilteringSection
              basicClassName={`${basicClassName}__inputsAndBtnsSection`}
            />
            <ButtonsSection
              basicClassName={`${basicClassName}__inputsAndBtnsSection`}
            />
          </div>
          <CharactersTable characters={characters} />
        </>
      )}
    </div>
  );
}

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