JavaScript中使用Promise调用API返回undefined问题求助

你的代码输出Promise { undefined }的核心原因是**getClosestSchachtInSeg函数没有返回任何异步操作的结果**，同时内部异步流程未正确处理。以下是具体问题分析和修正方案：

问题分析 #

1. getClosestSchachtInSeg被声明为async函数，但函数体内无return语句，默认返回Promise{undefined}
2. 内部pool.query()和fetch()等异步操作使用.then()链式调用，但未将结果传递出函数
3. 循环中的fetch未被等待，也未收集返回值，导致异步结果丢失

修正后的代码 #

第一步：修复getClosestSchachtInSeg函数 #

改用async/await简化异步流程，确保函数返回最终结果：

async function getClosestSchachtInSeg(
  LON,
  LAT,
  FROMANGLE,
  TOANGLE,
  NS,
  maxCount
) {
  try {
    const sqlQuery =
      "SELECT *, ST_X(ST_Transform (geom, 4326)) AS LON, ST_Y(ST_Transform (geom, 4326)) AS LAT," +
      " ST_Transform(SCHAECHTE_OWN.geom, 4326) <-> ST_SetSRID(ST_MakePoint(" +
      LON +
      ", " +
      LAT +
      "), 4326)::geometry AS dist " +
      ' FROM public."SCHAECHTE_OWN" SCHAECHTE_OWN ' +
      " WHERE atan((ST_X(ST_Transform (geom, 4326)) - " +
      LON +
      ") /  (ST_Y(ST_Transform (geom, 4326)) - " +
      LAT +
      ") > " +
      FROMANGLE +
      "*pi()/180" +
      " AND atan((ST_X(ST_Transform (geom, 4326)) - " +
      LON +
      ") /  (ST_Y(ST_Transform (geom, 4326)) - " +
      LAT +
      ") < " +
      TOANGLE +
      "*pi()/180" +
      " AND ST_Y(ST_Transform (geom, 4326)) " +
      NS +
      " " +
      LAT +
      " ORDER BY dist LIMIT " +
      maxCount +
      ";";

    // 等待SQL查询结果
    const results = await pool.query(sqlQuery);
    const resultList = [];

    if (results.rows.length > 0) {
      // 用map+Promise.all处理多个fetch请求
      const fetchPromises = results.rows.map(async (row) => {
        const ResLon = row.lon;
        const ResLat = row.lat;
        const ResDist = row.dist;

        const urlDistance =
          "http://gisdatavm01hw.versatel.local:5001/getShortestPathLonLatDistance/" +
          Math.round(LON * 1000000) / 1000000 +
          "/" +
          Math.round(LAT * 1000000) / 1000000 +
          "/" +
          Math.round(ResLon * 1000000) / 1000000 +
          "/" +
          Math.round(ResLat * 1000000) / 1000000;

        const response = await fetch(urlDistance);
        const body = await response.text();
        const Dist = JSON.parse(body)["distance"];
        
        // 返回包含目标浮点数的对象，可根据需求调整结构
        return {
          lon: ResLon,
          lat: ResLat,
          dist: ResDist,
          pathDistance: Dist || null
        };
      });

      // 等待所有fetch完成，收集结果
      const fetchedResults = await Promise.all(fetchPromises);
      resultList.push(...fetchedResults);
    }

    // 返回最终结果，使函数返回带数据的Promise
    return resultList;
  } catch (err) {
    console.error("Error executing query", err.stack);
    throw err; // 抛出错误供调用方捕获
  }
}

第二步：修复getClosestSchachtOWNJson12SegNew函数 #

使用Promise.all()等待所有异步调用完成，替代Promise.resolve()：

async function getClosestSchachtOWNJson12SegNew(request, response) {
  response.setHeader("Access-Control-Allow-Origin", "*");
  response.setHeader("Access-Control-Allow-Credentials", "true");
  response.setHeader(
    "Access-Control-Allow-Methods",
    "GET,HEAD,OPTIONS,POST,PUT"
  );
  response.setHeader(
    "Access-Control-Allow-Headers",
    "Access-Control-Allow-Headers, Origin,Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers"
  );

  const LON = request.params.LON;
  const LAT = request.params.LAT;
  const maxCount = request.params.maxCount;

  // 等待所有12个异步函数执行完成
  const values = await Promise.all([
    getClosestSchachtInSeg(LON, LAT, -90, -60, ">=", maxCount),
    getClosestSchachtInSeg(LON, LAT, -60, -30, ">=", maxCount),
    getClosestSchachtInSeg(LON, LAT, -30, 0, ">=", maxCount),
    getClosestSchachtInSeg(LON, LAT, 0, 30, ">=", maxCount),
    getClosestSchachtInSeg(LON, LAT, 30, 60, ">=", maxCount),
    getClosestSchachtInSeg(LON, LAT, 60, 90, ">=", maxCount),
    getClosestSchachtInSeg(LON, LAT, -90, -60, "<", maxCount),
    getClosestSchachtInSeg(LON, LAT, -60, -30, "<", maxCount),
    getClosestSchachtInSeg(LON, LAT, -30, 0, "<", maxCount),
    getClosestSchachtInSeg(LON, LAT, 0, 30, "<", maxCount),
    getClosestSchachtInSeg(LON, LAT, 30, 60, "<", maxCount),
    getClosestSchachtInSeg(LON, LAT, 60, 90, "<", maxCount),
  ]);

  console.log(values);
  // 如需返回给前端，可添加：response.json(values);
}

关键修正点 #

• 给getClosestSchachtInSeg添加return语句，传递异步操作结果
• 用await替代.then()，简化异步流程可读性
• 用Promise.all()处理循环中的多个fetch，确保所有异步操作完成后返回
• 在主函数中用Promise.all()等待所有子函数调用完成，而非直接包裹数组

内容的提问来源于stack exchange，提问作者CodeoDE