Convert milliseconds in to days,hours,minute, seconds

  
    var now = new Date(); // Return current date and time
    var future = new Date(now.setHours(now.getHours()+24));  // add 24 hours in present time .
    var diff = Math.abs(future - now); // return diff in milliseconds

    var secs = Math.floor(diff / 1000);
    var mins = Math.floor(secs / 60);
    secs = secs % 60;
    var hrs = Math.floor(mins / 60);
    mins = mins % 60;
    var days = Math.floor(hrs / 24);
    hrs = hrs % 24;

    str =    future.toString();
    str += '<br>'+days+' days '+hrs+' hours '+mins+' minutes '+secs+' seconds';

Substract date in js

 
    var now = new Date();
    //It will give the current date and time in default format.
 
    var future = new Date(now .setHours(now .getHours()+24));
    //in this we add 24 hours in present time .
 
    var diff = Math.abs(future - now);
 
   diff in milliseconds.

Parse Date in JS

var x = new Date(Date.parse("Jun 28 2012"));
 It will return :-
                     Wed Jun 27 2012 00:00:00 GMT+0530


And  var x = new Date(Date.parse("Jun 28 2012 14:00:00"));
 It will return :-
                     Wed Jun 28 2012 14:00:00 GMT+0530