如何等待函数在javascript中完成？

Question

如何在 JavaScript 中等待函数完成？ 我有 2 个函数 updateSeason 和 updateFixtures，我想等待第一个函数完成后再运行下一个函数。

我的两个函数都是异步的，它们工作得很好。唯一的问题是，如果我不使用setTimeout，我需要运行两次，因为updateFixture 在updateSeason 完成之前运行，并且在第一次运行时仍然没有要获取的文件。

更新数据

const updateData = async () => {
  await updateSeason();
  await updateFixtures();
};

更新季节

    // UPDATE SEASON
const updateSeason = async () => {
  // SEASONS TEMPLATE
  let seasonsTemplate = {
    timestamp: new Date(),
    season: null,
    leagues: [],
  };

  // FETCH LEAGUES INFO
  const leagues = await fetch(url + "leagues?subscribed=true&" + key)
    .then((response) => response.json())
    .then((data) => data.data);

  // MAP THROUGH LEAGUES
  leagues.map(async (league) => {
    const id = `${league.league_id}&`;

    // FETCH SEASONS INFO
    const seasons = await fetch(url + "seasons?league_id=" + id + key)
      .then((response) => response.json())
      .then((data) => data.data);

    // MAP THROUGH LEAGUES & POPULATE SEASONS TEMPLATE
    seasons.map((season) => {
      if (season.is_current) {
        seasonsTemplate.season = `${moment(season.start_date).format("YYYY")}_${moment(season.end_date).format("YYYY")}`;
        seasonsTemplate.leagues.push({
          country_id: season.country_id,
          league_id: league.league_id,
          league_name: league.name,
          season_id: season.season_id,
          start_date: season.start_date,
          end_date: season.end_date,
        });
      }
    });

    // CHECK / CREATE SEASON FOLDER
    const currentSeasonFolder = `./data/${seasonsTemplate.season}`;
    if (!existsSync(currentSeasonFolder)) {
      await mkdir(currentSeasonFolder);
      await mkdir(`${currentSeasonFolder}/matches`);
    }

    // CREATE / UPDATE SEASON FILES
    await writeFile("./data/current_season.json", JSON.stringify(seasonsTemplate));
    await writeFile(`${currentSeasonFolder}/season.json`, JSON.stringify(seasonsTemplate));

    console.log(`${league.name} updated...`);
  });
};

更新夹具

    // UPDATE FIXTURES
    const updateFixtures = async () => {
      // FIXTURES TEMPLATE
      let fixturesTemplate = {
        timestamp: new Date(),
        season: null,
        fixtures: [],
      };
    
      // FETCH CURRENT SEASON INFO
      const season = await fetch(api + "current_season.json").then((response) => response.json());
    
      // POPULATE FIXTURES TEMPLATE SEASON
      fixturesTemplate.season = season.season;
    
      // MAP THROUGH LEAGUES
      season.leagues.map(async (league) => {
        const id = `${league.season_id}&`;
    
        // FETCH COMPETITION FIXTURES
        const fixtures = await fetch(url + "matches?season_id=" + id + key)
          .then((response) => response.json())
          .then((data) => data.data);
    
       

 // MAP THROUGH FIXTURES & POPULATE FIXTURES TEMPLATE
    fixtures.map((match) => {
      if ((match.home_team.team_id === teamId || match.away_team.team_id === teamId) && match.status !== "postponed") {
        fixturesTemplate.fixtures.push({
          match_timestamp: new Date(match.match_start_iso).getTime(),
          match_start: match.match_start_iso,
          match_id: match.match_id,
          status: match.status === "" ? "notstarted" : match.status,
          home_team: getTeamName(match.home_team.team_id),
          home_short: getShortName(match.home_team.team_id),
          away_team: getTeamName(match.away_team.team_id),
          away_short: getShortName(match.away_team.team_id),
        });
      }
    });

    // SORT FIXTURES BY DATE IN ASCENDING ORDER
    fixturesTemplate.fixtures.sort((a, b) => a.match_timestamp - b.match_timestamp);

    // CREATE / UPDATE FIXTURES FILES
    const currentSeasonFolder = `./data/${season.season}`;
    await writeFile(currentSeasonFolder + "/fixtures.json", JSON.stringify(fixturesTemplate));

    console.log("Fixtures updated...");
  });
};

更新：

问题在于函数本身。 async Array.prototype.map 在 updateSeason 和 updateFixtures 两个函数中都替换为 for 循环，现在正在工作

Answer 1

您可以只对定义的函数使用 async/await，即使您不能在异步函数之外使用“await”关键字。

所以，例如，你有一个 index.js 文件，你可以这样做：

async function main() {
  await updateSeason();
  await updateFixtures();
}

main()

或直接调用简写函数

(async function main() {
  await updateSeason();
  await updateFixtures();
})()

无论如何，请避免在异步函数中使用“writeFileSync”或其他“同步”函数，因为这会阻塞事件循环并降低性能。

编辑：我现在看到您正在使用带有异步回调的 Array.prototype.map 函数，这可能是问题所在。

试试看这里：https://flaviocopes.com/javascript-async-await-array-map/

或者，否则，使用标准 for 循环来处理您的联赛

Answer 2

为什么不只是，

async function updateData() {
  await updatedSeason();
  await updateFixtures()
}

updateData();

Answer 3

Async Await 可以在这里为您提供帮助，因为它们都是异步函数。

const updateData = async () => {
  await updateSeason();
  await updateFixtures();
};

Answer 4

你忘了在函数前加上“await”

const updateData = async () => {
  // Add await before the functions because they are async functions
  await updateSeason()       
  await updateFixtures()
};