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Introducing Enhanced Alert Actions and Triage Functionality
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cron
Advanced tools
Package description
The cron npm package is used for scheduling tasks to be executed at specific times or intervals. It is inspired by the Unix cron scheduler and allows for the use of cron syntax to schedule tasks in a Node.js environment. This package is useful for setting up jobs like backups, sending emails, or cleaning up databases at regular intervals.
Basic Cron Job
This feature allows you to create a basic cron job that runs at a specified interval. In the provided code sample, a new CronJob is created that logs a message to the console every second.
"const CronJob = require('cron').CronJob;\nconst job = new CronJob('* * * * * *', function() {\n console.log('You will see this message every second');\n}, null, true, 'America/Los_Angeles');\njob.start();"
Time Zone Support
This feature demonstrates the ability to specify a time zone for the cron job. The code sample schedules a job to run at 11:30 AM, according to the 'America/New_York' time zone, from Monday to Friday.
"const CronJob = require('cron').CronJob;\nconst job = new CronJob('00 30 11 * * 1-5', function() {\n console.log('This runs at 11:30 AM (server time) every Monday through Friday.');\n}, null, true, 'America/New_York');\njob.start();"
Dynamic Job Scheduling
This feature allows for dynamic scheduling of jobs. The schedule can be updated or changed based on certain conditions or inputs. In the example, the 'dynamicSchedule' variable can be updated to change the job's schedule.
"const CronJob = require('cron').CronJob;\nlet dynamicSchedule = '00 30 11 * * 1-5'; // This can be dynamically changed\nconst job = new CronJob(dynamicSchedule, function() {\n console.log('This job's schedule can be dynamically changed.');\n}, null, true, 'America/Los_Angeles');\njob.start();"
node-schedule is a flexible cron-like and not-cron-like job scheduler for Node.js. It allows for more complex scheduling and includes features like job cancellation. It is a good alternative to cron when more flexibility is required.
Agenda is a job scheduling library for Node.js that uses MongoDB for job storage. It offers more robust job management features compared to cron, such as persistence, job prioritization, and repeating jobs. It's a good choice when jobs need to be managed across server restarts or in distributed systems.
Bull is a Redis-based queue system for Node.js. It is not a direct alternative to cron but can be used for scheduling through delayed jobs. It offers advanced features like job prioritization, concurrency control, and job events. Bull is suitable for applications requiring high reliability and real-time processing.
Changelog
v1.7.1 (2019-04-26)
Readme
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.
npm install cron
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.
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).
var CronJob = require('cron').CronJob;
new CronJob('* * * * * *', function() {
console.log('You will see this message every second');
}, null, true, 'America/Los_Angeles');
Note - You need to explicitly start a job in order to make it run. This gives a little more control over running your jobs.
There are more examples available in this repository at: /examples
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.
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.
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.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-40Parameter 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, 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 JS
Date 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 at
Moment 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 at
timers#timers_timeout_unref
from the NodeJS docs.start
- Runs your job.stop
- Stops your job.setTime
- Change 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 JS
Date
object.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.
MIT
FAQs
Cron jobs for your node
The npm package cron receives a total of 1,470,144 weekly downloads. As such, cron popularity was classified as popular.
We found that cron demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 3 open source maintainers collaborating on the project.
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