Calculate the difference between current date and age from personal ID

The goal is to show message for users that are less 25 years old. The personal ID consists of 081010333333, where 08year, 10month, 10date. I made code and it's very messy. So the question is: how to make it "right"? any advices and solutions are welcome. One on codepen and the code itself:



$('input').on('change keyup', function(i, el){
var d = new Date(),
getVal = $(this).val(),
getYear = $(this).val().slice(0,2),
getMonth = $(this).val().slice(2,4),
getDay = $(this).val().slice(4,6),
getCurrentYearFull = d.getFullYear(),
getCurrentMonth = ("0" + (d.getMonth() + 1)).slice(-2),
getCurrentDate = ("0" + (d.getDate())).slice(-2),
getCurrentYearShort = d.getFullYear().toString().slice(2,4);

if(getYear > getCurrentYearShort){
getYear = "19" + getYear
} else {
getYear = "20" + getYear
}
var yearDiff = getCurrentYearFull - getYear;
if (yearDiff >=10 && $('input').val().length >= 4) {
if(getCurrentMonth >= getMonth){
if (getCurrentDate >= getDay){
$(".check").text('good')
}
else {
$(".check").text('bad')
}
} else {
$(".check").text('bad')
}
} else {
$(".check").text('bad')

}
$('.test').text(yearDiff)
})




In this answer I'll just reveiw the way you calculate the age difference.
So first, I would like to mention, that you should really work with four-digit numbers for displaing years - if that's possible for you.

In the suggestion below you'll see, that I don't compare the years, months and days because comparing two timestamps is better!
So you just have to feed the is25YearsOld function with a yyyymmdd-date and it will tell if you are older/younger than 25.



function is25YearsOld(input) {
// the date of birth of a 25 year old
var dob25 = new Date();
// setFullYear to the current year (eg. 2016) and subtract 25
dob25.setFullYear(dob25.getFullYear() - 25);
// set the time to midnight
dob25.setHours(0);
dob25.setMinutes(0);
dob25.setSeconds(0);
// get the unix-timestamp
dob25 = dob25.getTime();
// the user's date of birth
var dob = new Date();
// set the year, month and day accordingly to the input
dob.setFullYear(parseInt(input.substr(0, 4)));
dob.setMonth(parseInt(input.substr(4, 2)) - 1); // (-1) because month is zero-based
dob.setDate(parseInt(input.substr(6, 2)));
// set the time to midnight
dob.setHours(0);
dob.setMinutes(0);
dob.setSeconds(0);
// get the unix-timestamp
dob = dob.getTime();
// if the timestamp of requiredDateOfBirth is smaller than the one of dateOfBirth, the user is too young
return dob25 >= dob;
}

// Oct 10, 2008
document.getElementById("test1").innerHTML = is25YearsOld("20081010") ? "You are old enough!" : "You are too young!";
// Oct 10, 1988
document.getElementById("test2").innerHTML = is25YearsOld("19881010") ? "You are old enough!" : "You are too young!";

2008-10-10:

1988-10-10:

StackExchange Code Review Q#124330, answer score: 2