Getting datetimes from cron format using javascript

This isn't much help, but it's a start. There are some java (not javascript) and php solutions that have some decent code that you'd want to translate and incorporate if you end up writing this yourself.

Take a look at these two bits of code:

http://www.redmoon.ch/?p=39

http://www.phpclasses.org/package/2568-PHP-Parse-cron-tab-files-to-retrieve-job-schedules.html

HTH

You might want to check out Later.js which can parse a Cron expression and calculate the next occurrences.

var schedule = cronParser().parse('* */5 * * * *', true);
var results = later(60).get(schedule, 100, startDate, endDate);

One can use cron-parser lib. More info here