📆 mi-cron

mi-cron is a microscopic (~1KB minified & gzipped) parser for standard cron expressions.

Features

• Supports the complete standard cron syntax
• Supports some convenient syntax extensions: @-shorthands (@daily) and steps (*/10)
• Can compute the next scheduled date for a given expression
• Tiny & dependency-free

Installation

npm i @cheap-glitch/mi-cron

Usage

const { parseCron } = require('@cheap-glitch/mi-cron');

console.log(parseCron.nextDate('*/5 6-12 3 3 *').toUTCString());
// Wed, 03 Mar 2021 06:00:00

API

parseCron(exp: string): CronSchedule

Parses a standard cron expression. Supports:

• globs (*)
• ranges (0-30, mon-fri)
• steps (*/3, 20-31/2, 10/5)
• lists (1,15, 0-10,20-30/2)
• @-shorthands (@weekly)

Does NOT support:

• L, W, #, ?, H
• year field
• @reboot

Returns an object with all possible values for each field (minutes, hours, days, months and days of the week), or undefined if the expression is invalid (wrong syntax, unsupported instruction, impossible range, etc).

const { parseCron } = require('@cheap-glitch/mi-cron');

console.log(parseCron('*/5 6-10 1,15 * wed'));
// {
// 	minutes:  [0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55],
// 	hours:    [6, 7, 8, 9, 10],
// 	days:     [1, 15],
// 	months:   [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12],
// 	weekDays: [3],
// }

parseCron.nextDate(exp: string | CronSchedule[, from: Date = new Date.now()]): Date

Takes a cron schedule or expression and returns the next date that matches the schedule, or undefined if the expression is invalid. If given a datetime as the second argument, it will start the computation from this time (otherwise it will use the current datetime at the moment it's called).

const { parseCron } = require('@cheap-glitch/mi-cron');

console.log(parseCron.nextDate('* * * * *', new Date('01 Jan 2020 00:00:00 GMT')).toUTCString());
// Wed, 01 Jan 2020 00:01:00

// Get the next five scheduled dates
const schedule = parseCron('@weekly');
const nextDate = new Date();
for (let i=0; i<5; i++) {
	console.log(nextDate = parseCron.nextDate(schedule, nextDate));
}

Changelog

See the full changelog here.

Contributing

Contributions are welcomed! Please open an issue before submitting substantial changes.

Related

• crontab.guru – Interactive cron schedule editor
• Description of the crontab format
• Best practices for cron

License

ISC