[JavaScript] 現在幾歲年齡算法

 

   const todayDate = getTodayDate();

   function getTodayDate() {

      const fullDate = new Date();

      const yyyy = fullDate.getFullYear();

      const MM =

        fullDate.getMonth() + 1 >= 10

          ? fullDate.getMonth() + 1

          : '0' + (fullDate.getMonth() + 1);

      const dd =

        fullDate.getDate() < 10 ? '0' + fullDate.getDate() : fullDate.getDate();

      const today = String(yyyy) + String(MM) + String(dd);

      return today;

    }

輸入值為西元年月日共8碼

     let ageGap: number;

        const todayYYYY = Number(todayDate.slice(0, 4));

        const todayMM = Number(todayDate.slice(4, 6));

        const todayDD = Number(todayDate.slice(6, 8));

        const birthYYYY = Number(birthDay.slice(0, 4));

        const birthMM = Number(birthDay.slice(4, 6));

        const birthDD = Number(birthDay.slice(6, 8));

        let calcYYYY: number;

        let calcMM: number;

        let calcDD: number;

        calcYYYY = todayYYYY - birthYYYY;

        calcMM = todayMM - birthMM;

        if (calcMM < 1) {

          if (calcMM < 0) {

            calcYYYY -= 1;

          } else {

            calcDD = todayDD - birthDD;

            if (calcDD < 0) {

              calcYYYY -= 1;

            }

          }

        }

        ageGap = Number(calcYYYY);