JS date addition and subtraction, date operation code_time and date

1. The date minus the number of days equals the second date

function cc(dd,dadd){
//可以加上错误处理
var a = new Date(dd)
a = a.valueOf()
a = a - dadd * 24 * 60 * 60 * 1000
a = new Date(a)
alert(a.getFullYear() + "年" + (a.getMonth() + 1) + "月" + a.getDate() + "日")
}
cc("12/23/2002",2)

I have to make supplements here, wasting a lot of time to draw lessons:
Javascript code for time
Numbers 0-11 represent January-December: var a= new Date(2006,5,6) The result is 2006-6-6
0-6 means day of the week
1-31 represents the date
0-23 hours
0-59 minutes, seconds

Two. //The difference between two dates (d1 - d2).

function DateDiff(d1,d2){
  var day = 24 * 60 * 60 *1000;
try{  
    var dateArr = d1.split("-");
  var checkDate = new Date();
    checkDate.setFullYear(dateArr[0], dateArr[1]-1, dateArr[2]);
  var checkTime = checkDate.getTime();
 
  var dateArr2 = d2.split("-");
  var checkDate2 = new Date();
    checkDate2.setFullYear(dateArr2[0], dateArr2[1]-1, dateArr2[2]);
  var checkTime2 = checkDate2.getTime();
  
  var cha = (checkTime - checkTime2)/day; 
    return cha;
  }catch(e){
  return false;
}
}//end fun

3. Application: