Install

npm install cron-parser

yarn add cron-parser

cron-parser

Node.js library for parsing and manipulating crontab instructions. It includes support for timezones and DST transitions.

Compatibility
Node >= 12.0.0
TypeScript >= 4.2

Setup

 npm install cron-parser

Supported format

*    *    *    *    *    *
┬    ┬    ┬    ┬    ┬    ┬
│    │    │    │    │    |
│    │    │    │    │    └ day of week (0 - 7, 1L - 7L) (0 or 7 is Sun)
│    │    │    │    └───── month (1 - 12)
│    │    │    └────────── day of month (1 - 31, L)
│    │    └─────────────── hour (0 - 23)
│    └──────────────────── minute (0 - 59)
└───────────────────────── second (0 - 59, optional)

Supports mixed use of ranges and range increments (W character not supported currently). See tests for examples.

Usage

Simple expression.

 var parser = require('cron-parser');

try {
  var interval = parser.parseExpression('*/2 * * * *');

  console.log('Date: ', interval.next().toString()); // Sat Dec 29 2012 00:42:00 GMT+0200 (EET)
  console.log('Date: ', interval.next().toString()); // Sat Dec 29 2012 00:44:00 GMT+0200 (EET)

  console.log('Date: ', interval.prev().toString()); // Sat Dec 29 2012 00:42:00 GMT+0200 (EET)
  console.log('Date: ', interval.prev().toString()); // Sat Dec 29 2012 00:40:00 GMT+0200 (EET)
} catch (err) {
  console.log('Error: ' + err.message);
}

Iteration with limited timespan. Also returns ES6 compatible iterator (when iterator flag is set to true).

 var parser = require('cron-parser');

var options = {
  currentDate: new Date('Wed, 26 Dec 2012 12:38:53 UTC'),
  endDate: new Date('Wed, 26 Dec 2012 14:40:00 UTC'),
  iterator: true
};

try {
  var interval = parser.parseExpression('*/22 * * * *', options);

  while (true) {
    try {
      var obj = interval.next();
      console.log('value:', obj.value.toString(), 'done:', obj.done);
    } catch (e) {
      break;
    }
  }

  // value: Wed Dec 26 2012 14:44:00 GMT+0200 (EET) done: false
  // value: Wed Dec 26 2012 15:00:00 GMT+0200 (EET) done: false
  // value: Wed Dec 26 2012 15:22:00 GMT+0200 (EET) done: false
  // value: Wed Dec 26 2012 15:44:00 GMT+0200 (EET) done: false
  // value: Wed Dec 26 2012 16:00:00 GMT+0200 (EET) done: false
  // value: Wed Dec 26 2012 16:22:00 GMT+0200 (EET) done: true
} catch (err) {
  console.log('Error: ' + err.message);
}

Timezone support

 var parser = require('cron-parser');

var options = {
  currentDate: '2016-03-27 00:00:01',
  tz: 'Europe/Athens'
};

try {
  var interval = parser.parseExpression('0 * * * *', options);

  console.log('Date: ', interval.next().toString()); // Date:  Sun Mar 27 2016 01:00:00 GMT+0200
  console.log('Date: ', interval.next().toString()); // Date:  Sun Mar 27 2016 02:00:00 GMT+0200
  console.log('Date: ', interval.next().toString()); // Date:  Sun Mar 27 2016 04:00:00 GMT+0300 (Notice DST transition)
} catch (err) {
  console.log('Error: ' + err.message);
}

Manipulation

 var parser = require('cron-parser');

var interval = parser.parseExpression('0 7 * * 0-4');
var fields = JSON.parse(JSON.stringify(interval.fields)); // Fields is immutable
fields.hour = [8];
fields.minute = [29];
fields.dayOfWeek = [1,3,4,5,6,7];
var modifiedInterval = parser.fieldsToExpression(fields);
var cronString = modifiedInterval.stringify();
console.log(cronString); // "29 8 * * 1,3-7"

Options

currentDate - Start date of the iteration
endDate - End date of the iteration

currentDate and endDate accept string, integer and Date as input.

In case of using string as input, not every string format accepted
by the Date constructor will work correctly.
The supported formats are:

The reason being that those are the formats accepted by the
luxon library which is being used to handle dates.

Using Date as an input can be problematic specially when using the tz option. The issue being that, when creating a new Date object without
any timezone information, it will be created in the timezone of the system that is running the code. This (most of times) won't be what the user
will be expecting. Using one of the supported string formats will solve the issue(see timezone example).

iterator - Return ES6 compatible iterator object
utc - Enable UTC
tz - Timezone string. It won't be used in case utc is enabled

Last weekday of the month

This library supports parsing the range 0L - 7L in the weekday position of
the cron expression, where the L means "last occurrence of this weekday for
the month in progress".

For example, the following expression will run on the last monday of the month
at midnight:

0 0 0 * * 1L

The library also supports combining L expressions with other weekday
expressions. For example, the following cron will run every Monday as well
as the last Wednesday of the month: