我只是对下面的代码有疑问。if 语句无法正常工作，它们没有正确测试月份。我相信问题出在不等于部分。使用脚本这似乎是问题所在。在这方面，我不是 100% 熟悉 javascript 语法。谢谢
<script = text/javascript>
function calculate(){
var year = parseInt(document.getElementById("year").value);
var month = parseInt(document.getElementById("month").value);
var day = parseInt(document.getElementById("day").value);
if ((month == 2 && day > 28) && (!(year == 2016) || (!(year == 2020))) && day > 28)
{
alert("Sorry. The day " + day + " is not available in the month of February in the year of " + year);
}
else if((month == 2 && day > 29) && ((year == 2016) || (year == 2020))){
alert("Sorry. The day " + day + " is not available in the month of February in the year of " + year);
}
else
{
newmonth = month + 9;
newday = day + 10;
//if the month is greater then 12 roll over the year and change the month
if ((newmonth > 12)){
year = year + 1;
newmonth = newmonth - 12;
}
//if the day equals January and has a day grater than 31 then roll over to the next month
if ((newday > 31) && (newmonth == 1)){
newmonth = newmonth + 1;
newday = newday - 31;
}
//if the day equals February and has a day grater than 28 on a non leap year then roll over to the next month
if ((newday > 28) && (newmonth == 2) && (year == 2014)){
newmonth = newmonth + 1;
newday = newday - 28;
}
//if the day equals February and has a day grater than 29 then roll over to the next month
if ((newday > 29) && (newmonth == 2) && (year == 2016)){
newmonth = newmonth + 1;
newday = newday - 29;
}
//if the day equals February and has a day grater than 29 then roll over to the next month
if ((newday > 29) && (newmonth == 2) && (year == 2020)){
newmonth = newmonth + 1;
newday = newday - 29;
}
//if the day equals February and has a day grater than 29 then roll over to the next month
if ((newday > 29) && (newmonth == 2) && (year == 2024)){
newmonth = newmonth + 1;
newday = newday - 29;
}
//if the day equals February and has a day grater than 29 then roll over to the next month
if ((newday > 29) && (newmonth == 2) && (year == 2028)){
newmonth = newmonth + 1;
newday = newday - 29;
}
//if the day equals March and has a day grater than 31 then roll over to the next month
if ((newday > 31) && (newmonth == 3)){
newmonth = newmonth + 1;
newday = newday - 31;
}
//if the day equals April and has a day grater than 30 then roll over to the next month
if ((newday > 30) && (newmonth == 4)){
newmonth = newmonth + 1;
newday = newday - 30;
}
//if the day equals May and has a day grater than 31 then roll over to the next month
if ((newday > 31) && (newmonth == 5)){
newmonth = newmonth + 1;
newday = newday - 31;
}
//if the day equals June and has a day grater than 30 then roll over to the next month
if ((newday > 30) && (newmonth == 6)){
newmonth = newmonth + 1;
newday = newday - 30;
}
//if the day equals July and has a day grater than 31 then roll over to the next month
if ((newday > 31) && (newmonth == 7)){
newmonth = newmonth + 1;
newday = newday - 31;
}
//if the day equals March and has a day grater than 31 then roll over to the next month
if ((newday > 31) && (newmonth == 8)){
newmonth = newmonth + 1;
newday = newday - 31;
}
//if the day equals September and has a day grater than 30 then roll over to the next month
if ((newday > 30) && (newmonth == 9)){
newmonth = newmonth + 1;
newday = newday - 30;
}
//if the day equals October and has a day grater than 31 then roll over to the next month
if ((newday > 31) && (newmonth == 10)){
newmonth = newmonth + 1;
newday = newday - 31;
}
//if the day equals November and has a day grater than 30 then roll over to the next month
if ((newday > 30) && (newmonth == 11)){
newmonth = newmonth + 1;
newday = newday - 30;
}
//if the day equals December and has a day grater than 31 then roll over to the next month
if ((newday > 31) && (newmonth == 12)){
newmonth = 1;
newday = newday - 31;
}
alert("Your cow is due to calve on:"+" Day "+newday+" Month "+newmonth+" Year "+year);
}
}