To get days since epoch, you need to use Math.abs() JavaScript method. Then use the Math.Floor() method to get the difference between dates since epoch and current date −
Example
<html>
<head>
<title>JavaScript Clone Date</title>
</head>
<body>
<script>
var current_date, epocDate;
current_date = new Date();
document.write("Current Date: "+current_date);
var epocDate = new Date(new Date().getTime() / 1000);
document.write("<br>Since epoch: "+epocDate);
var res = Math.abs(current_date - epocDate) / 1000;
// get total days between two dates
var days = Math.floor(res / 86400);
document.write("<br>Difference (Days): "+days);
</script>
</body>
</html>Output
Current Date: Fri May 25 2018 15:42:43 GMT+0530 (India Standard Time) Since epoch: Sun Jan 18 1970 21:44:03 GMT+0530 (India Standard Time) Difference (Days): 17658