단순로직 테스트.

function isValidByArray(arg) {
    if (arg instanceof Array) {
      if (arg.filter(e => typeof e !== "number").length === 0) {
        return true;
      }
    }
    return false;
  }

  function setSymbol(num, sym) {
    if (typeof num !== "number") {
      throw new Error("Parameters is wrong.");
    }

    let strNum = String(num);
    let strFraction = "";
    if (strNum.indexOf(".") !== -1) {
      // 소수점인 경우.
      const splitNum = strNum.split(".");
      strNum = splitNum[0];
      strFraction = splitNum[1];
    }

    // console.log(strNum, strFraction);
    let len = strNum.length;
    const cnt = Math.floor((strNum.length - 1) / 3);

    // 숫자가 3자리 이하인경우
    if (len < 3) {
      return strFraction !== "" ? strNum + "." + strFraction : strNum;
    }

    let retStr = "";
    for (let i = 0; i < cnt; i++) {
      // 뒤에서부터 3자리씩 추출.
      const splitStr = strNum.substr(-3);
      strNum = strNum.substr(0, len - (i + 1) * 3);
      retStr = sym + splitStr + retStr;

      // 만약 0 < n <= 3 사이로 마지막 loop인 경우.
      if (0 < strNum.length && strNum.length <= 3) {
        retStr = strNum + retStr;
      }
    }

    console.log(strFraction, retStr);
    if (strFraction !== "") {
      retStr = retStr + "." + strFraction;
    }

    return retStr;
  }

  function sum(a, b) {
    // a와 b를 따로 구함.
    let calA, calB;

    console.log(a, typeof a);
    if (typeof a === "number") {
      calA = a;
    } else if (isValidByArray(a)) {
      calA = a.reduce((p, c) => p + c, 0);
    } else if (typeof a === "function") {
      if (typeof a() === "number") {
        calA = a();
      } else {
        throw new Error("Parameters is wrong.");
      }
    } else {
      throw new Error("Parameters is wrong.");
    }

    if (typeof b === "number") {
      calB = b;
    } else if (isValidByArray(b)) {
      calB = b.reduce((p, c) => p + c, 0);
    } else if (typeof b === "function") {
      if (typeof b() === "number") {
        calB = b();
      } else {
        throw new Error("Parameters is wrong.");
      }
    } else {
      throw new Error("Parameters is wrong.");
    }

    console.log(calA, calB);
    const result = setSymbol(calA + calB, ",");
    return result;
    // return 0;
  }