<!DOCTYPE html>
<html>
<body>
<p>Click the button to calculate the number of years since midnight, January 1, 1970.</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
function myFunction() {
var minutes = 1000 * 60;
var hours = minutes * 60;
var days = hours * 24;
var years = days * 365;
var t = Date.now();
var y = Math.round(t / years);
document.getElementById("demo").innerHTML = y;
}
</script>
</body>
</html>