Stub JS Date

date_stub.js

var lastNow         = new Date();
var lastStubbedNow  = new Date(1421224206 * 1000);

var oldDate         = Date;

// stub with new Date function
Date = function () {
  var args = arguments.length > 0 ? Array.prototype.slice.call(arguments) : [getStubbedNow().getTime()];
  args.unshift(null)
  return new ( Function.prototype.bind.apply( oldDate, args ) ) // http://stackoverflow.com/a/8843181/1036829
}

// delegate to oldDate's methods
var attributes = Object.getOwnPropertyNames(oldDate);
for (var i = 0, attr; attr = attributes[i]; i++) {
  if ( oldDate.hasOwnProperty(attr) ) {
    Date[attr] = (function(attr){
      return oldDate[attr]
    })(attr);
  }
}

// stub Date.now as well
Date.now = function() {
  return getStubbedNow();
}

function getStubbedNow(){
  var now    = new oldDate();
  var offset = now - lastNow;
  return new oldDate(lastStubbedNow.getTime() + offset);
}