Handling AWS Crons using Local Dates with EventCronParser

UTC to local. Local back to UTC.

Crons are typically stored in UTC. Since I deploy Planda through ECS, and ECS uses UTC, my crons need to work with UTC. However, the dates displayed to users must be local dates, and users need to be able to edit these cron dates.

The challenge is to convert UTC dates to local dates, so my users can view these dates and make changes. Then, I have to take these changes, and convert them back into UTC for storage and usage on the server-side.

Some methods of EventCronParser

desc(): Returns a description of your cron, described using local time.

next(from?: Date | number): Returns the next date after from, or the date after the date returned by the previous function call to next(), if no parameter is supplied.

range(start: Date | number, end: Date | number): Returns all cron dates within the range given.

Example: Days of the week with forms

import EventCronParser from 'event-cron-parser'

const cronParser = new EventCronParser("0 7 ? * MON,WED,FRI *")
const localDaysOfWeek = cronParser.getLocalDays()

// Show users localDaysOfWeek, and allow them to make changes.
const editedLocalDaysOfWeek = ...

cronParser.setDaysOfWeek(editedLocalDaysOfWeek)
// Voila! The UTC cron has now been adjusted according to the local dates given.

// Return the new cron with:
const adjustedCron = cronParser.getCron()

Further functionalities

Durations

EventCronParser can also store durations, and can therefore return all event dates that occur sometime during given interval with range(start: Date | number, end: Date | number, inclusive?: boolean), when inclusive=true. If only events fully contained in this interval are wanted, set inclusive=false (default).

AWS rate expressions

EventCronParser doesn't only handle crons – it can also handle AWS rate expressions. Just pass a rate expression in, and we will detect it automatically.

const rateParser = new EventCronParser("rate(1 day)")
const nextDate = rateParser.next(Date.now())

Cron/Rate expression validation

Calling validate() will throw an error if the cron or rate expression is invalid. Invalid crons are allowed to be passed into EventCronParser for cron/rate building purposes, but should be validated before being usage.