Date Difference in Javascript

Question

I am developing a system which requires that you should be at least 18 years old to register.

For doing this validation i have implemented date difference in javascript in following way, but it is not accurate, is there any javascript function or other way to do this?

var d1=new Date(1985,1,28);
var d2=new Date();
var milli=d2-d1;
var milliPerYear=1000*60*60*24*365.26;
var years_old=milli/milliPerYear;

Any client side validation can easily be circumvented. Always validate on the server side. Although in this case, you cannot even ensure that a person provides his real birthday. — Felix Kling
– Felix Kling, Commented Jan 28, 2012 at 11:03
Yeah - this is more of a user-consent liability issue, rather than a full credit check or anything. Client-side validation is fine. — cloudfeet
– cloudfeet, Commented Nov 28, 2014 at 14:24

PeeHaa · Accepted Answer · 2014-05-07 18:01:52Z

8

Legally being at least 18 years old is not about the amount of time corresponding to the average duration of 18 years (years aren't always the same length). It is about the current date being after your 18th birth date. Hence, you should just add 18 to the year count on the birthdate and see if this is before or after the present date, e.g.

var birthDate = new Date(1985,1,28);
var today = new Date();
if (today >= new Date(birthDate.getFullYear() + 18, birthDate.getMonth(), birthDate.getDate())) {
  // Allow access
} else {
  // Deny access
}

You should do the same validation on the server side as well.

Note that this also handles people born on 29th February the correct way: in this case JavaScript will create a date object to represent the 1st March 18 years later.

edited May 7, 2014 at 18:01

PeeHaa

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answered Jan 28, 2012 at 11:03

Adam Zalcman

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8 Comments

Sam Greenhalgh Over a year ago

Important point. We don't celebrate our birthdays by counting the milliseconds since we were born.

Adam Zalcman Over a year ago

@mack Yes, why would you expect otherwise?

mack Over a year ago

sorry,

var birthDate = new Date(1994,1,27); var today = new Date(); if (today >= new Date(birthDate.getFullYear() + 18, birthDate.getMonth(), birthDate.getDay())) {   alert("Allow"); } else {   alert("Deny"); }

try this, it alerts deny

Adam Zalcman Over a year ago

@mack That's right. I mistyped the name of day-of-month accessor: it was getDay() while it should be getDate(). Corrected now. Thanks!

mack Over a year ago

var birthDate = new Date(1994,1,27); var today = new Date(); if (today >= new Date(birthDate.getFullYear() + 18, birthDate.getMonth(), birthDate.getDate())) {   alert("Allow"); } else {   alert("Deny"); }

still alert deny

|

Malk · Accepted Answer · 2012-01-28 11:14:59Z

1

I like http://momentjs.com/

<script src="moment.min.js"></script>
<script>
  var dob = new moment([1985,1,28]);
  var age = new.moment().diff(dob, 'years')

  if (age >= 18) { 
    ...
  }
</script>

answered Jan 28, 2012 at 11:14

Malk

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1 Comment

mack Over a year ago

var dob = new moment([1985,1,30]); var age = new moment().diff(dob, 'years') alert(age); it alerts 27

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