var date_getPointDate = function (currDate, num) {  //num表示天数，接受正负数  if(!num){
   //做num简单验证    return currDate;  }  num = Math.floor(num);  var symbol = '/';  if(currDate.indexOf('-')>-1){    symbol = '-';    currDate = currDate.replace(/-/g,'/');  }else if(currDate.indexOf('.') > -1){    symbol = '.';    currDate = currDate.replace(/\./g,'/');  }  //symbol = '-'; //定制输出分隔符  var myDate = new Date(currDate),      lw = new Date(Number(myDate) + 1000 * 60 * 60 * 24 * num), //num天数      lastY = lw.getFullYear(),      lastM = lw.getMonth()+1,      lastD = lw.getDate(),      startdate=lastY+ symbol +(lastM<10 ? "0" + lastM : lastM)+ symbol +(lastD<10 ? "0"+ lastD : lastD);  return startdate;}console.log(date_getPointDate("2017.10.24", 30))  //2017-11-23console.log(date_getPointDate("2017-10-24", -30)) //2017/09/24/*  * 调用规则 : * 指定日期n天前日期：date_getPointDate("2017/11/26", -30) * 指定日期n天后日期：date_getPointDate("2017/10/27", 30) */