如何在substr javascript中调整日期构造函数

Question

如果你看看我的日期验证，当我来测试它是否在过去时，它是有效的，尽管日期构造函数期望零日期月份，那么我如何从表示月份的子字符串值中减去一（从结果中减去一，而不是位置）

//start of datefield
var dateformat=/^(?:(?:31/(?:0[13578]|1[02])|(?:29|30)/(?:0[13-9]|1[012])|(?:0[1-9]|1d|2[0-8])/(?:0[1-9]|1[0-2]))/[2-9]d{3}|29/02/(?:[2-9]d(?:0[48]|[2468][048]|[13579][26])|(?:[2468][048]|[3579][26])00))$/;
if (!date.match(dateformat))
{
      errors.push("format incorrect use dd/mm/yyyy make sure you are entering correct days to the month remember 30 days have september, april, june & november, only 28 days in february unless leap year next is 2016");
}
var today = new Date();
var courseYear =date.substr(6,4) // use substr or substring to capture the last four digits
var courseMonth =date.substr(3,2) // use substr or substring to capture the four and fifth digits
var courseDay = date.substr(0,2)//e the first and second digits
var dateToCompare = new Date(courseYear, courseMonth, courseDay);
if (dateToCompare < today) {
  errors.push("this date is in the past"); 
}

Answer 1

那么我如何减去一个

使用减法运算符"-"和数字文字"1"。它还可以将字符串转换为之前的数字。对于年份和日期，您可以使用一元加号显式地进行转换（尽管Date构造函数隐式进行转换）：

new Date(+courseYear, courseMonth-1, +courseDay);