Does anyone have any solid examples of how to implement a jQuery or javascript based age checker? I'm looking to send someone to a page where they need to enter in the Day, Month and Year at least once a day when they hit any page on the site. Once they validate as 18 then they would not be pestered again until the next day if they return.
Any ideas?
A cookie-based solution does seem a logical fit since you can programmatically modify them from JavaScript and you can set their expiry. Calculating the date in pure JavaScript can be done as such:
var millisPerYear = 1000 * 60 * 60 * 24 * 365;
var birthdate = new Date(year, month, day); // from user input.
var age = ((new Date().getTime()) - birthdate.getTime()) / millisPerYear;
// Now set the "age" cookie.
All that is left is for your server-side response handlers to return content conditionally based on the value of the "age" cookie from the request agent.
There seem to be a number of existing resources on the web for implementing similar functionality. All of them create a cookie with the birth day selector which held by the user and can be set to expire a day later. Obviously this can be a problem if your users don't have cookies enabled. Below are a couple of examples.
http://www.webdesignforums.net/php-67/age_verification_script-30188/index2.html
http://www.techerator.com/2010/09/how-to-perform-age-verification-with-jquery-and-cookies-mmm-cookies/
There is a wonderful Date library for JavaScript called DateJS. It makes date operations extremely simple.
Your first step is, of course, to parse the date that is provided. DateJS provides a lot of parsing functionalities, such as:
Date.parse("Mar 3 2010");
Date.parse('March 20th 1973');
Date.parse("03 12 2010");
Once you have parsed the date, you can compare it to the date 18 years ago. This is also easy with DateJS
var userBDay = Date.parse("Mar 3 1970");
var eighteenYearsAgo = (18).years().ago();
var is18 = (userBDay >= eighteenYearsAgo);
You are of course assuming the user is honest. Not to mention JS can be disabled, or modified client side. But that is an entirely different discussion.
EDIT: Had forgotten about your mention of only doing verification once a day. This would require either:
