How to calculate based on the year of the month and day?

Question

I want to calculate the age based on the year of the month and day. How can I achieve this?

function getAge( dateString ) {
    var today = new Date('2019-23-05');
    const d = today.getDay();
    var birthDate = new Date(dateString);
    var age = today.getFullYear() - birthDate.getFullYear();
    var m = today.getMonth() - birthDate.getMonth();
    if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
        age--;
    }
    return age;
}

console.log(getAge('1997-04-23'));

Answer 1

You made a small mistake with the line var today = new Date('2019-23-05').

Change the month and day as the following, that will work for your case to have 2019-05-23:

function getAge( dateString ) {
    var today = new Date('2019-05-23');
    const d = today.getDay();
    var birthDate = new Date(dateString);
    var age = today.getFullYear() - birthDate.getFullYear();
    var m = today.getMonth() - birthDate.getMonth();
    if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
        age--;
    }
    return age;
}

console.log(getAge('1997-04-23'));

Hope this helps!

Answer 2

Here is a simple solution:

function getAge(dateString) {
   var ageInMilliseconds = new Date() - new Date(dateString);
   return Math.floor(ageInMilliseconds/1000/60/60/24/365); // convert to years
}
console.log(getAge('1997-04-23'));

Answer 3

I'd just use a one liner like this:

const getAge = (dateString) => new Date(new Date().getTime() - new Date(dateString).getTime()).getUTCFullYear() - 1970
console.log(getAge('1997-04-23'));