JSON.parse(str)

will not convert date string to date object and we get an error

let str = '{"title":"Conference","date":"2017-11-30T12:00:00.000Z"}';

let meetup = JSON.parse(str);

document.write( meetup.date.getDate() ); // Error!

The value of

meetup.date

is a string, not a

Date

object. That is why

JSON.parse

was unable to transform that string into a

Date

object. ... Passing the reviving function to

JSON.parse

as the second argument fixes the issue. The reviving function returns all values “as is”, but

date

will become a

Date

object and the error will not occur

let str = '{"title":"Conference","date":"2017-11-30T12:00:00.000Z"}';

let meetup = JSON.parse(str, function(key, value) {
  if (key == 'date') return new Date(value);
  return value;
});

alert( meetup.date.getDate() ); // now works!