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node-cron

by kelektiv

kelektiv /node-cron

Cron for NodeJS.

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node-cron

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Cron is a tool that allows you to execute something on a schedule. This is typically done using the cron syntax. We allow you to execute a function whenever your scheduled job triggers. We also allow you to execute a job external to the javascript process using

child\_process

. Additionally, this library goes beyond the basic cron syntax and allows you to supply a Date object. This will be used as the trigger for your callback. Cron syntax is still an acceptable CronTime format. Although the Cron patterns supported here extend on the standard Unix format to support seconds digits, leaving it off will default to 0 and match the Unix behavior.

Installation

npm install cron

If You Are Submitting Bugs/Issues

Because we can't magically know what you are doing to expose an issue, it is best if you provide a snippet of code. This snippet need not include your secret sauce, but it must replicate the issue you are describing. The issues that get closed without resolution tend to be the ones without code examples. Thanks.

Versions and Backwards compatibility breaks:

As goes with semver, breaking backwards compatibility should be explicit in the versioning of your library. As such, we'll upgrade the version of this module in accordance with breaking changes (I'm not always great about doing it this way so if you notice that there are breaking changes that haven't been bumped appropriately please let me know).

Usage (basic cron usage):

var CronJob = require('cron').CronJob; var job = new CronJob( '\* \* \* \* \* \*', function() { console.log('You will see this message every second'); }, null, true, 'America/Los\_Angeles' ); // Use this if the 4th param is default value(false) // job.start()

Note - You don't need to explicitly start a job in order to make it run since the 4th parameter is set to

true

. However, by default you need to call

job.start()

to start the cron job, which gives a little more control over running your jobs.

There are more examples available in this repository at:/examples

Available Cron patterns:

Asterisk. E.g. \* Ranges. E.g. 1-3,5 Steps. E.g. \*/2

Read up on cron patterns here. Note the examples in the link have five fields, and 1 minute as the finest granularity, but this library has six fields, with 1 second as the finest granularity.

There are tools that help when constructing your cronjobs. You might find something like https://crontab.guru/ or https://cronjob.xyz/ helpful. But, note that these don't necessarily accept the exact same syntax as this library, for instance, it doesn't accept the

seconds

field, so keep that in mind.

Cron Ranges

When specifying your cron values you'll need to make sure that your values fall within the ranges. For instance, some cron's use a 0-7 range for the day of week where both 0 and 7 represent Sunday. We do not. And that is an optimisation.

  • Seconds: 0-59
  • Minutes: 0-59
  • Hours: 0-23
  • Day of Month: 1-31
  • Months: 0-11 (Jan-Dec)
  • Day of Week: 0-6 (Sun-Sat)

Gotchas

  • Millisecond level granularity in JS or moment date objects. Because computers take time to do things, there may be some delay in execution. This should be on the order of milliseconds. This module doesn't allow MS level granularity for the regular cron syntax, but does allow you to specify a real date of execution in either a javascript date object or a moment object. When this happens you may find that you aren't able to execute a job that_should_ run in the future like with
    new Date().setMilliseconds(new Date().getMilliseconds() + 1)
    . This is due to those cycles of execution above. This wont be the same for everyone because of compute speed. When I tried it locally I saw that somewhere around the 4-5 ms mark was where I got consistent ticks using real dates, but anything less than that would result in an exception. This could be really confusing. We could restrict the granularity for all dates to seconds, but felt that it wasn't a huge problem so long as you were made aware. If this becomes more of an issue, We can revisit it.
  • Arrow Functions for
    onTick
    Arrow functions get their
    this
    context from their parent scope. Thus, if you use them, you will not get the
    this
    context of the cronjob. You can read a little more in this ticket GH-40

API

Parameter Based

  • job
    • shortcut to
      new cron.CronJob()
      .
  • time
    • shortcut to
      new cron.CronTime()
      .
  • sendAt
    • tells you when a
      CronTime
      will be run.
  • timeout
    • tells you when the next timeout is.
  • CronJob
    • constructor(cronTime, onTick, onComplete, start, timezone, context, runOnInit, utcOffset, unrefTimeout)
    • Of note, the first parameter here can be a JSON object that has the below names and associated types (see examples above).
    • cronTime
    • [REQUIRED] - The time to fire off your job. This can be in the form of cron syntax or a JSDate object.
    • onTick
    • [REQUIRED] - The function to fire at the specified time. If an
      onComplete
      callback was provided,
      onTick
      will receive it as an argument.
      onTick
      may call
      onComplete
      when it has finished its work.
    • onComplete
    • [OPTIONAL] - A function that will fire when the job is stopped with
      job.stop()
      , and may also be called by
      onTick
      at the end of each run.
    • start
    • [OPTIONAL] - Specifies whether to start the job just before exiting the constructor. By default this is set to false. If left at default you will need to call
      job.start()
      in order to start the job (assuming
      job
      is the variable you set the cronjob to). This does not immediately fire your
      onTick
      function, it just gives you more control over the behavior of your jobs.
    • timeZone
    • [OPTIONAL] - Specify the timezone for the execution. This will modify the actual time relative to your timezone. If the timezone is invalid, an error is thrown. You can check all timezones available atMoment Timezone Website. Probably don't use both.
      timeZone
      and
      utcOffset
      together or weird things may happen.
    • context
    • [OPTIONAL] - The context within which to execute the onTick method. This defaults to the cronjob itself allowing you to call
      this.stop()
      . However, if you change this you'll have access to the functions and values within your context object.
    • runOnInit
    • [OPTIONAL] - This will immediately fire your
      onTick
      function as soon as the requisite initialization has happened. This option is set to
      false
      by default for backwards compatibility.
    • utcOffset
    • [OPTIONAL] - This allows you to specify the offset of your timezone rather than using the
      timeZone
      param. Probably don't use both
      timeZone
      and
      utcOffset
      together or weird things may happen.
    • unrefTimeout
    • [OPTIONAL] - If you have code that keeps the event loop running and want to stop the node process when that finishes regardless of the state of your cronjob, you can do so making use of this parameter. This is off by default and cron will run as if it needs to control the event loop. For more information take a look attimers#timers_timeout_unreffrom the NodeJS docs.
    • start
    • Runs your job.
    • stop
    • Stops your job.
    • setTime
    • Stops and changes the time for the
      CronJob
      . Param must be a
      CronTime
      .
    • lastDate
    • Tells you the last execution date.
    • nextDates
    • Provides an array of the next set of dates that will trigger an
      onTick
      .
    • fireOnTick
    • Allows you to override the
      onTick
      calling behavior. This matters so only do this if you have a really good reason to do so.
    • addCallback
    • Allows you to add
      onTick
      callbacks.
  • CronTime
    • constructor(time)
    • time
    • [REQUIRED] - The time to fire off your job. This can be in the form of cron syntax or a JSDateobject.

Contributions

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 I'll just say thanks.

License

MIT

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