Json 파일의 데이터 가공 (JavaScript) [부제: reduce]

const res = await fetch('http://localhost:3000/data');
const json = await res.json();

const division = (arr, n) => {
  const length = arr.length;
  const divide = Math.floor(length / n) + (Math.floor(length % n) > 0 ? 1 : 0);
  const newArray = [];
  for (let i = 0; i <= divide; i++) {
    newArray.push(arr.splice(0, n));
  }
  return newArray;
};
const dividedData = division(json, 7);
let arr = [];
let timestampArr = [];
let result;
dividedData.forEach((weeklyData) => {
  if (weeklyData.length) {
    result = weeklyData.reduce((a, c) => {
      timestampArr.push(c.timestamp);
      c.dailyEC2Stats.forEach((eachData, idx) => {
        if (eachData.region in a) {
          a[eachData.region] = {
            countTotalEC2: a[eachData.region].countTotalEC2 + eachData.countTotalEC2,
            countUnmanagedEC2: a[eachData.region].countUnmanagedEC2 + eachData.countUnmanagedEC2,
            countUnallowedSpec: a[eachData.region].countUnallowedSpec + eachData.countUnallowedSpec,
          };
        } else { // 1️⃣
          a[eachData.region] = {
            countTotalEC2: eachData.countTotalEC2,
            countUnmanagedEC2: eachData.countUnmanagedEC2,
            countUnallowedSpec: eachData.countUnallowedSpec,
          };
        }
      });
      return a;
    }, {});
    arr.push(result);
  }
});
const timestampDivided = division(timestampArr, 7);
const weeklyTimestampArr = [];
timestampDivided.forEach((timestamp) => {
  if (timestamp[0] !== undefined) {
    const obj = {
      start: `${timestamp[0]}`,
      end: `${timestamp[timestamp.length - 1]}`,
    };
    weeklyTimestampArr.push(obj);
  }
});

let resultArr = [];
arr.forEach((data) => {
  let dataObj = { // 2️⃣
    datas: {
      timestamp: {
        start: '',
        end: '',
      },
      weeklyEC2Stats: [],
    },
  };

  const obj = Object.entries(data).map(([key, value]) => ({
    region: key,
    AvgOfCountTotalEC2: Math.floor(value.countTotalEC2 / 7),
    AvgOfCountUnmanagedEC2: Math.floor(value.countUnmanagedEC2 / 7),
    AvgOfCountUnallowedSpec: Math.floor(value.countUnallowedSpec / 7),
  }));
  dataObj['datas']['weeklyEC2Stats'].push(...obj);
  resultArr.push(dataObj);
});
resultArr.forEach((result, idx1) => {
  weeklyTimestampArr.forEach((weeklyTimestamp, idx2) => {
    if (idx1 === idx2) {
      result['datas']['timestamp'] = weeklyTimestamp;
    }
  });
});
const file = 'weekly_stats_ec2_datas_v1.json';
fs.writeFile(file, JSON.stringify(resultArr), (err) => {
  if (err) {
    console.error(err);
  }
});