Cron Validator

Cron Validator is a util that allows you to validate a cron expression, similar to what crontab guru does, but in your code base.

Alternatives

• cron-validate: It has more features and configuration options to restrict ranges, or create presets of configs. It includes an AWS preset that should match AWS Schedule Expressions.

Installation

npm install cron-validator

Usage

Require syntax:

1const cron = require('cron-validator');
2
3if (cron.isValidCron('* * * * *')) {
4    // Do something
5}

Or import syntax with TypeScript:

1import { isValidCron } from 'cron-validator'
2
3if (isValidCron('* * * * *')) {
4    // Do something
5}

Support for seconds can be enabled by passing the seconds flag as true in options:

1const cron = require('cron-validator');
2
3cron.isValidCron('* * * * * *');
4// false
5
6cron.isValidCron('* * * * * *', { seconds: true });
7// true

The same goes to enable the alias support for months and weekdays:

1const cron = require('cron-validator');
2
3cron.isValidCron('* * * * mon');
4// false
5
6cron.isValidCron('* * * * mon', { alias: true });
7// true

Likewise, the allowBlankDay flag can be enabled to mark days or weekdays blank with a ? symbol:

1const cron = require('cron-validator');
2
3cron.isValidCron('* * * * ?');
4// false
5
6cron.isValidCron('* * * * ?', { allowBlankDay: true });
7// true

The allowSevenAsSunday flag can be enabled to enable support for digit 7 as Sunday:

1const cron = require('cron-validator');
2
3cron.isValidCron('* * * * 7');
4// false
5
6cron.isValidCron('* * * * 7', { allowSevenAsSunday: true });
7// true

The allowNthWeekdayOfMonth flag can be enabled to enable expressions denoting n-th weekday of the month:

1const cron = require('cron-validator');
2
3cron.isValidCron('* * * * tue#2');
4// false
5
6cron.isValidCron('* * * * tue#2', { allowNthWeekdayOfMonth: true }); // second Tuesday of each month
7// true

Features

• Support seconds.
• Support alias.
• Support blank day notation with ? symbol.
• Support both 0-6 and 1-7 ranges for weekdays.
• Support n-th weekday of month such as TUE#2
• Have an explain mode returning the fragments in error.

Motivations

Many great cron libraries already exists on NPM, why this one?

Libraries like node-cron are primarily made to schedule jobs using a cron expression, not validate those cron expressions. They come with additional behaviors not always required. They also bring their own set of defaults which might be in conflicts with the defaults of other external systems. We needed something to validate an expression before sending it off to an external system, so we created this to be a little more strict and configurable, with a more specific behavior.

We decided to go for the naive approach first, which results in lenghty code and tests, but also making it easier to reason about cron expressions and their specific rules.