javascript - 通过 Node js 将数据更新到 firebase 项目列表时检查更新结果

Question

我想通过 Node js 将一些数据添加到 firebase 中的项目列表中，但我不知道如何检查更新过程是否失败。这是我的工具:

// set data to json 
let servicesJson = {
    "car_services": [services],
    "car_services_status": 1
}
// add car service to province
let provinceIdNumber = parseInt(provinceId, 10);
var areaRef = db.ref("areas")
areaRef.orderByChild('province_id').equalTo(provinceIdNumber).once('value', function (areaSnapshots) {
    if (areaSnapshots.val() != null) {
        var result = true 
        areaSnapshots.forEach (function (child) {
            let currentTime = new Date().toISOString();
            servicesJson.last_updated = currentTime
            child.ref.update(servicesJson, function (error) {
                if (error) {
                    console.log("*** error ***")
                    result = false
                } else {
                    console.log("*** success ***")
                    result = true
                }
            }) 
        });
        console.log("*** finished ***")
        res.send({ 'success': result });
    } else {
        res.send({ 'success': false, 'error_code': 'CSTP05', 'error_msg': 'Cant find any area of province to update car service' });
    }
});

这是日志:

*** finished ***
*** success ***
*** success ***
*** success ***
*** success ***

如何等到循环结束再返回结果？

Answer 1

使用Promise

// set data to json
let servicesJson = {
  car_services: [services],
  car_services_status: 1
};
// add car service to province
let provinceIdNumber = parseInt(provinceId, 10);
var areaRef = db.ref("areas");
const updatePromise = new Promise((resolve, reject) => {
  const changedCount = 0;
  areaRef
    .orderByChild("province_id")
    .equalTo(provinceIdNumber)
    .once("value", function(areaSnapshots) {
      if (areaSnapshots.val() != null) {
        areaSnapshots.forEach(function(child) {
          let currentTime = new Date().toISOString();
          servicesJson.last_updated = currentTime;
          child.ref.update(servicesJson, function(error) {
            if (error) {
              changedCount++;
              console.log("*** error ***");
            } else {
              changedCount++;
              console.log("*** success ***");
            }
          });

          if (areaSnapshots.length === changedCount) {
            console.log("*** finished ***");
            resolve({ success: true });
          }
        });
      } else {
        reject({
          success: false,
          error_code: "CSTP05",
          error_msg: "Cant find any area of province to update car service"
        });
      }
    });
});

updatePromise
  .then(data => {
    res.send(data);
  })
  .catch(error => {
    res.send(error);
  });