From another answer on Stackoverflow is a conversion from Javascript date to .net DateTime:
long msSinceEpoch = 1260402952906; // Value from Date.getTime() i
This method is working for me:
public sCdateToJsDate(cSDate: any): Date {
// cSDate is '2017-01-24T14:14:55.807'
var datestr = cSDate.toString();
var dateAr = datestr.split('-');
var year = parseInt(dateAr[0]);
var month = parseInt(dateAr[1])-1;
var day = parseInt(dateAr[2].substring(0, dateAr[2].indexOf("T")));
var timestring = dateAr[2].substring(dateAr[2].indexOf("T") + 1);
var timeAr = timestring.split(":");
var hour = parseInt(timeAr[0]);
var min = parseInt(timeAr[1]);
var sek = parseInt(timeAr[2]);
var date = new Date(year, month, day, hour, min, sek, 0);
return date;
}