kelektiv
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 cronTable of Contents
- Features
- Installation
- Migrating
- Basic Usage
- Cron Patterns
- API
- Gotchas
- Community
- Contributing
- Acknowledgements
- License
⬆ Migrating
v4 dropped Node v16 and renamed the job.running property:
Dropped Node version
Node v16 is no longer supported. Upgrade your Node installation to Node v18 or above
Property renamed and now read-only
You can no longer set the running property (now isActive). It is read-only. To start or stop a cron job, use job.start() and job.stop().
v3 introduced TypeScript and tighter Unix cron pattern alignment:
Month & day-of-week indexing changes
Month Indexing: Changed from
0-11to1-12. So you need to increment all numeric months by 1.Day-of-Week Indexing: Support added for
7as Sunday.
Adjustments in CronJob
- The constructor no longer accepts an object as its first and only params. Use
CronJob.from(argsObject)instead. - Callbacks are now called in the order they were registered.
nextDates(count?: number)now always returns an array (empty if no argument is provided). UsenextDate()instead for a single date.
Removed methods
removed
job()method in favor ofnew CronJob(...args)/CronJob.from(argsObject)removed
time()method in favor ofnew CronTime()
🛠 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 usingjob.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 unitsDetailed 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 aCronTimewill execute (returns a LuxonDateTimeobject).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 aCronTimewill 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 withvalidanderrorproperties).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, waitForCompletion, errorHandler, name, threshold):
cronTime: [REQUIRED] - The time to fire off your job. Can be cron syntax, a JSDateobject or a LuxonDateTimeobject.onTick: [REQUIRED] - Function to execute at the specified time. If anonCompletecallback was provided,onTickwill receive it as an argument.onComplete: [OPTIONAL] - Invoked when the job is halted withjob.stop(). It might also be triggered byonTickpost its run.start: [OPTIONAL] - Determines if the job should commence before constructor exit. Default isfalse.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 theonTickfunction post initialization. Default isfalse.utcOffset: [OPTIONAL] - Specifies time zone offset in minutes. Cannot co-exist withtimeZone.unrefTimeout: [OPTIONAL] - Useful for controlling event loop behavior. More details here.waitForCompletion: [OPTIONAL] - Iftrue, no additional instances of theonTickcallback 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 isfalse.errorHandler: [OPTIONAL] - Function to handle any exceptions that occur in theonTickmethod.name: [OPTIONAL] - Name of the job. Useful for identifying jobs in logs.threshold: [OPTIONAL] - Threshold in ms to control whether to execute or skip missed execution deadlines caused by slow or busy hardware. Execution delays within threshold will be executed immediately, and otherwise will be skipped. In both cases a warning will be printed to the console with the job name and cron expression. See issue #962 for more information. Default is250.
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 theCronJob. Parameter must be aCronTime.lastDate: Provides the last execution date.nextDate: Indicates the subsequent date that will activate anonTick.nextDates(count): Supplies an array of upcoming dates that will initiate anonTick.fireOnTick: Allows modification of theonTickcalling behavior.addCallback: Permits addition ofonTickcallbacks.
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 totimeZonefromCronJobparameters.utcOffset: [OPTIONAL] - Analogous toutcOffsetfromCronJobparameters.
💢 Gotchas
Both JS
Dateand LuxonDateTimeobjects don't guarantee millisecond precision due to computation delays. This module excludes millisecond precision for standard cron syntax but allows execution date specification through JSDateor LuxonDateTimeobjects. 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
onTickbinds them to the parent'sthiscontext. As a result, they won't have access to the cronjob'sthiscontext. 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