What is cron-parser?
The cron-parser npm package is a utility for parsing crontab instructions. It allows users to interpret cron schedule expressions and calculate the next run times for jobs. It is useful for scheduling tasks in Node.js applications.
What are cron-parser's main functionalities?
Parsing Cron Expressions
This feature allows users to parse a cron expression and get the next execution times. The code sample demonstrates how to parse a cron expression that runs every 2 minutes and log the next execution time.
const cronParser = require('cron-parser');
try {
const interval = cronParser.parseExpression('*/2 * * * *');
console.log('Date: ', interval.next().toString()); // Get the next date
} catch (err) {
console.error('Error: ' + err.message);
}
Iterating Over Execution Times
This feature allows users to iterate over the execution times of a cron job. The code sample demonstrates how to get the next 5 execution times for a cron expression that runs at the start of every hour.
const cronParser = require('cron-parser');
try {
const interval = cronParser.parseExpression('0 * * * *');
for (let i = 0; i < 5; i++) {
console.log('Date: ', interval.next().toString()); // Get the next 5 dates
}
} catch (err) {
console.error('Error: ' + err.message);
}
Handling Cron Expression with Timezone
This feature allows users to parse a cron expression with a specific timezone. The code sample demonstrates how to parse a cron expression that runs at the start of every hour, considering the timezone of Europe/Amsterdam.
const cronParser = require('cron-parser');
try {
const options = {
currentDate: new Date('Wed, 26 Dec 2012 14:38:53 GMT'),
tz: 'Europe/Amsterdam'
};
const interval = cronParser.parseExpression('0 * * * *', options);
console.log('Date: ', interval.next().toString()); // Get the next date considering timezone
} catch (err) {
console.error('Error: ' + err.message);
}
Other packages similar to cron-parser
node-cron
node-cron is a task scheduler in pure JavaScript for Node.js based on cron syntax. It allows you to schedule tasks to be executed at specific times or intervals. It is similar to cron-parser but also includes the ability to execute the jobs, not just parse cron expressions.
node-schedule
node-schedule is a flexible cron-like and not-cron-like job scheduler for Node.js. It allows for more complex scheduling than standard cron expressions, offering a higher level of customization. It is similar to cron-parser in parsing cron expressions but also provides an extensive job scheduling system.
bree
bree is a job scheduler for Node.js with cron and human-friendly syntax. It supports cron expressions and allows for scheduling jobs with additional features like job timeouts and concurrency control. Bree is more feature-rich compared to cron-parser, which focuses solely on parsing cron expressions.
agenda
agenda is a light and flexible job scheduling library for Node.js. It uses MongoDB for job storage and offers features like job prioritization, concurrency, and repeating jobs. While cron-parser is focused on parsing cron expressions, agenda provides a full job scheduling system with persistence.
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());
console.log('Date: ', interval.next().toString());
console.log('Date: ', interval.prev().toString());
console.log('Date: ', interval.prev().toString());
} 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;
}
}
} 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());
console.log('Date: ', interval.next().toString());
console.log('Date: ', interval.next().toString());
} 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.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);
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:
0 0 0 * * 1,3L