js 计算某个日期加月份最后月份不会增加或者跳变

/**

 *

 * @param {*} dateString 原来日期 2023-12-31  

 * @param {*} months 加月份  2

 * @returns  2024-02-29

 */

export function getDateByMonth(dateString, months=0) {

  console.log(1);

  let oldMonths = dateString.substring(0,7);

  let day = dateString.substring(8);

  let myDate = new Date(oldMonths);//传进来日期加月份的第一天

  myDate.setMonth(myDate.getMonth()+1+months);

  myDate.setDate(0);

  let sMonth = "00" + (myDate.getMonth() + 1);

  sMonth = sMonth.slice(-2);

  let sDay = "00" + myDate.getDate();

  sDay = sDay.slice(-2);

  if(day>sDay){

    return myDate.getFullYear() + "-" + sMonth + "-" + sDay;

  }else{

    return myDate.getFullYear() + "-" + sMonth + "-" + day;

  }

}