How To Calculated Age For Date of Birth Using JavaScript

Create a file age.js and fill it with this code:

<!-- CHANGE ME -->
var DOB = "August 31, 1998";

var millisecondsBetweenDOBAnd1970 = Date.parse(DOB);
var millisecondsBetweenNowAnd1970 = Date.now();
var ageInMilliseconds = millisecondsBetweenNowAnd1970-millisecondsBetweenDOBAnd1970;
//--We will leverage Date.parse and now method to calculate age in milliseconds refer here https://www.w3schools.com/jsref/jsref_parse.asp

var milliseconds = ageInMilliseconds;
var second = 1000;
var minute = second*60;
var hour = minute*60;
var day = hour*24;
var month = day*30; 

//using 30 as base as months can have 28, 29, 30 or 31 days depending a month in a year it itself is a different piece of comuptation*/
var year = day*365;

//let the age conversion begin
var years = Math.round(milliseconds/year);
var months = years*12;
var days = years*365;
var hours = Math.round(milliseconds/hour);
var seconds = Math.round(milliseconds/second);


function printResults(){
var message = ""+years;
document.getElementById('age').innerHTML = message;
}

window.onload = printResults;

<html>
<head>
   <title>
     EXAMPLE
   </title>
</head>

<body>

<!-- Start HTML Body/CSS →

    Age: <span id="age"></span>

<!-- End HTML Body/CSS →

<script src="../age.js"></script>

</body>
</html>

Put the age.js script into your index.html inside the body tag, before </body>.

Still confused? Feel free to contact me.