cron is a robust tool for running jobs (functions or commands) on schedules defined using the cron syntax.
Perfect for tasks like data backups, notifications, and many more!

Cron for Node.js

🌟 Features

• execute a function whenever your scheduled job triggers
• execute a job external to the javascript process (like a system command) using child_process
• use a Date or Luxon DateTime object instead of cron syntax as the trigger for your callback
• use an additional slot for seconds (leaving it off will default to 0 and match the Unix behavior)

🚀 Installation

npm install cron

Table of Contents

1. Features
2. Installation
3. Migrating
4. Basic Usage
5. Cron Patterns
   • Cron Syntax Overview
   • Supported Ranges
6. API
   • Standalone Functions
   • CronJob Class
   • CronTime Class
7. Gotchas
8. Community
   • Join the Community
9. Contributing
   • General Contribution
   • Submitting Bugs/Issues
10. Acknowledgements
11. License

⬆ Migrating

v4 dropped Node v16 and renamed the job.running property:

v3 introduced TypeScript and tighter Unix cron pattern alignment:

🛠 Basic Usage

import { CronJob } from 'cron';

const job = new CronJob(
	'* * * * * *', // cronTime
	function () {
		console.log('You will see this message every second');
	}, // onTick
	null, // onComplete
	true, // start
	'America/Los_Angeles' // timeZone
);
// job.start() is optional here because of the fourth parameter set to true.

// equivalent job using the "from" static method, providing parameters as an object
const job = CronJob.from({
	cronTime: '* * * * * *',
	onTick: function () {
		console.log('You will see this message every second');
	},
	start: true,
	timeZone: 'America/Los_Angeles'
});

Note: In the first example above, the fourth parameter to CronJob() starts the job automatically. If not provided or set to falsy, you must explicitly start the job using job.start().

For more advanced examples, check the examples directory.

⏰ Cron Patterns

Cron patterns are the backbone of this library. Familiarize yourself with the syntax:

- `*` Asterisks: Any value
- `1-3,5` Ranges: Ranges and individual values
- `*/2` Steps: Every two units

Detailed patterns and explanations are available at crontab.org. The examples in the link have five fields, and 1 minute as the finest granularity, but our cron scheduling supports an enhanced format with six fields, allowing for second-level precision. Tools like crontab.guru can help in constructing patterns but remember to account for the seconds field.

Supported Ranges

Here's a quick reference to the UNIX Cron format this library uses, plus an added second field:

field          allowed values
-----          --------------
second         0-59
minute         0-59
hour           0-23
day of month   1-31
month          1-12 (or names, see below)
day of week    0-7 (0 or 7 is Sunday, or use names)

Names can also be used for the 'month' and 'day of week' fields. Use the first three letters of the particular day or month (case does not matter). Ranges and lists of names are allowed.
Examples: "mon,wed,fri", "jan-mar".

📖 API

Standalone Functions

• sendAt: Indicates when a CronTime will execute (returns a Luxon DateTime object).

  import * as cron from 'cron';
  
  const dt = cron.sendAt('0 0 * * *');
  console.log(`The job would run at: ${dt.toISO()}`);
  

• timeout: Indicates the number of milliseconds in the future at which a CronTime will execute (returns a number).

  import * as cron from 'cron';
  
  const timeout = cron.timeout('0 0 * * *');
  console.log(`The job would run in ${timeout}ms`);
  

• validateCronExpression: Validates if a given cron expression is valid (returns an object with valid and error properties).

  import * as cron from 'cron';
  
  const validation = cron.validateCronExpression('0 0 * * *');
  console.log(`Is the cron expression valid? ${validation.valid}`);
  if (!validation.valid) {
  	console.error(`Validation error: ${validation.error}`);
  }
  

CronJob Class

Constructor

constructor(cronTime, onTick, onComplete, start, timeZone, context, runOnInit, utcOffset, unrefTimeout):

• cronTime: [REQUIRED] - The time to fire off your job. Can be cron syntax, a JS Date object or a Luxon DateTime object.

• onTick: [REQUIRED] - Function to execute at the specified time. If an onComplete callback was provided, onTick will receive it as an argument.

• onComplete: [OPTIONAL] - Invoked when the job is halted with job.stop(). It might also be triggered by onTick post its run.

• start: [OPTIONAL] - Determines if the job should commence before constructor exit. Default is false.

• timeZone: [OPTIONAL] - Sets the execution time zone. Default is local time. Check valid formats in the Luxon documentation.

• context: [OPTIONAL] - Execution context for the onTick method.

• runOnInit: [OPTIONAL] - Instantly triggers the onTick function post initialization. Default is false.

• utcOffset: [OPTIONAL] - Specifies time zone offset in minutes. Cannot co-exist with timeZone.

• unrefTimeout: [OPTIONAL] - Useful for controlling event loop behavior. More details here.

• waitForCompletion: [OPTIONAL] - If true, no additional instances of the onTick callback function will run until the current onTick callback has completed. Any new scheduled executions that occur while the current callback is running will be skipped entirely. Default is false.

• errorHandler: [OPTIONAL] - Function to handle any exceptions that occur in the onTick method.

Methods

• from (static): Create a new CronJob object providing arguments as an object. See argument names and descriptions above.

• start: Initiates the job.

• stop: Halts the job.

• setTime: Modifies the time for the CronJob. Parameter must be a CronTime.

• lastDate: Provides the last execution date.

• nextDate: Indicates the subsequent date that will activate an onTick.

• nextDates(count): Supplies an array of upcoming dates that will initiate an onTick.

• fireOnTick: Allows modification of the onTick calling behavior.

• addCallback: Permits addition of onTick callbacks.

Properties

• isActive: [READ-ONLY] Indicates if a job is active (checking to see if the callback needs to be called).

• isCallbackRunning: [READ-ONLY] Indicates if a callback is currently executing.

  const job = new CronJob('* * * * * *', async () => {
  	console.log(job.isCallbackRunning); // true during callback execution
  	await someAsyncTask();
  	console.log(job.isCallbackRunning); // still true until callback completes
  });
  
  console.log(job.isCallbackRunning); // false
  job.start();
  console.log(job.isActive); // true
  console.log(job.isCallbackRunning); // false
  

CronTime Class

Constructor

constructor(time, zone, utcOffset):

• time: [REQUIRED] - The time to initiate your job. Accepts cron syntax or a JS Date object.

• zone: [OPTIONAL] - Equivalent to timeZone from CronJob parameters.

• utcOffset: [OPTIONAL] - Analogous to utcOffset from CronJob parameters.

💢 Gotchas

• Both JS Date and Luxon DateTime objects don't guarantee millisecond precision due to computation delays. This module excludes millisecond precision for standard cron syntax but allows execution date specification through JS Date or Luxon DateTime objects. However, specifying a precise future execution time, such as adding a millisecond to the current time, may not always work due to these computation delays. It's observed that delays less than 4-5 ms might lead to inconsistencies. While we could limit all date granularity to seconds, we've chosen to allow greater precision but advise users of potential issues.

• Using arrow functions for onTick binds them to the parent's this context. As a result, they won't have access to the cronjob's this context. You can read a little more in issue #47 (comment).

🤝 Community

Join the Discord server! Here you can discuss issues and get help in a more casual forum than GitHub.

🌍 Contributing

This project is looking for help! If you're interested in helping with the project, please take a look at our contributing documentation.

🐛 Submitting Bugs/Issues

Please have a look at our contributing documentation, it contains all the information you need to know before submitting an issue.

🙏 Acknowledgements

This is a community effort project. In the truest sense, this project started as an open source project from cron.js and grew into something else. Other people have contributed code, time, and oversight to the project. At this point there are too many to name here so we'll just say thanks.

Special thanks to Hiroki Horiuchi, Lundarl Gholoi and koooge for their work on the DefinitelyTyped typings before they were imported in v2.4.0.

⚖ License

MIT