How can I validate that someone is over 18 from their date of birth?

Question

I am doing validation for Driver's Date of birth, it should be minimum of 18 from the current date.

var Dates = $get('<%=ui_txtDOB.ClientID %>');   
var Split = Dates.value.split("/");

if (parseInt(Split[2]) > 1993) 
{
    alert("DOB year should be less than 1993");
    Dates.focus();
    return false;
}  

I am using this above JavaScript validation for checking a person's DOB above 18, but it is not correct. I need to check with today's date and it should be above 18. How can I compare and check with the current date?

Answer 1

Try this.

var enteredValue = $get('<%=ui_txtDOB.ClientID %>');;
var enteredAge = getAge(enteredValue.value);
if( enteredAge > 18 ) {
    alert("DOB not valid");
    enteredValue.focus();
    return false;
}

Using this function.

function getAge(DOB) {
    var today = new Date();
    var birthDate = new Date(DOB);
    var age = today.getFullYear() - birthDate.getFullYear();
    var m = today.getMonth() - birthDate.getMonth();
    if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
        age--;
    }    
    return age;
}

Demo here: http://jsfiddle.net/codeandcloud/n33RJ/

Answer 2

My approach is to find the date 18 (or any number) years ago from today, then see if that's after (greater) than their dob. By setting all values to date objects it makes the comparison easy.

function is_of_age(dob, age) {
  // dates are all converted to date objects
  var my_dob = new Date(dob);
  var today = new Date();
  var max_dob = new Date(today.getFullYear() - age, today.getMonth(), today.getDate());
  return max_dob.getTime() > my_dob.getTime();
}

Because the Date object can parse strings in a variety of formats, You don't have to worry too much about where dob is coming from. Simply call is_of_age("1980/12/4", 18); or is_of_age("2005-04-17", 13); or basically any string format or numeric that can be parsed as a Date parameter.