JavaScript program to take birth year and tells age

Following program shows you how to take birth year and tells age.
In this program we get birth year from user and tells their age using currentYear - birthYear

var birthYear  = prompt("Please enter your date of birth:");
var age = new Date().getFullYear() - birthYear;
 console.log("Your age is " + age);

Output:

Please enter your date of birth:
1990
Your age is 28