JSON is a great format for serializing data, but unfortunately it does not support dates.
If you serialize an object that contains date fields using JSON.stringify, the dates will be converted to strings. If you then parse the same object using JSON.parse, the date fields will remain strings.
The solution for this problem is to use a 'reviver' function in the call to JSON.parse that will inspect the strings and convert those that look like dates into date objects.