Trigger functions and/or evaluate cron expressions in JavaScript. No dependencies. Most features. Node. Deno. Browser.

Try it live on jsfiddle.

Croner

• Trigger functions in JavaScript using Cron syntax.
• Find first date of next month, find date of next tuesday, etc.
• Pause, resume or stop execution after a task is scheduled.
• Works in Node.js >=4.0 (both require and import).
• Works in Deno >=1.16.
• Works in browsers as standalone, UMD or ES-module.
• Experimental feature: Schedule in specific target timezones.
• Includes TypeScript typings.

Quick examples:

// Basic: Run a function at the interval defined by a cron expression
const job = Cron('*/5 * * * * *', () => {
    console.log('This will run every fifth second');
});

// Enumeration: What dates do the next 100 sundays occur at?
const nextSundays = Cron('0 0 0 * * 7').enumerate(100);
console.log(nextSundays);

// Days left to a specific date
const msLeft = Cron('59 59 23 24 DEC *').next() - new Date();
console.log(Math.floor(msLeft/1000/3600/24) + " days left to next christmas eve");

// Run a function at a specific date/time using a non-local timezone (time is ISO 8601 local time)
// This will run 2023-01-23 00:00:00 according to the time in Asia/Kolkata
Cron('2023-01-23T00:00:00', { timezone: 'Asia/Kolkata' }, () => { console.log('Yay') });

More examples...

Why another javascript cron implementation

Because the existing ones aren't good enough. They have serious bugs, use bloated dependencies, do not work in all environments and/or simply don't work as expected.

Benchmark at 2022-02-01:

> node cron-implementation-test.js

Test: When is next monday in october, pattern '0 0 0 * 10 1'

node-schedule: 2022-10-03 00:00:00 in 15.26ms
node-cron:     ???                 in 1.076ms
cron:          2022-11-07 00:00:00 in 2.923ms
croner:        2022-10-03 00:00:00 in 1.774ms

Test: When is next 15th of february, pattern '0 0 0 15 2 *'

node-schedule: 2022-02-15 00:00:00 in 13.306ms
node-cron:     ???                 in 1.676ms
cron:          2022-03-15 00:00:00 in 6.066ms
croner:        2022-02-15 00:00:00 in 0.575ms

Test: When is 23:00 next 31st march, pattern '0 0 23 31 3 *'

node-schedule: 2022-03-31 23:00:00 in 18.894ms
node-cron:     ???                 in 3.017ms
Month '3' is limited to '30' days.
cron:          2022-04-01 23:00:00 in 4.508ms
croner:        2022-03-31 23:00:00 in 1.381ms

https://gist.github.com/Hexagon/703f85f2dd86443cc17eef8f5cc6cb70

Installation

Node.js

npm install croner --save

JavaScript

// ESM Import ...
import Cron from "croner";

// ... or CommonJS Require
const Cron = require("croner");

TypeScript

Note that only default export is available in Node.js TypeScript, as the commonjs module is used internally.

import Cron from "croner";

const scheduler : Cron = new Cron("* * * * * *", () => {
    console.log("This will run every second.");
});

Deno

JavaScript

import Cron from "https://cdn.jsdelivr.net/gh/hexagon/croner@4/src/croner.js";

Cron("* * * * * *", () => {
    console.log("This will run every second.");
});

TypeScript

import { Cron } from "https://cdn.jsdelivr.net/gh/hexagon/croner@4/src/croner.js";

const _scheduler : Cron = new Cron("* * * * * *", () => {
    console.log("This will run every second.");
});

Browser

Manual

• Download latest zipball
• Unpack
• Grab croner.min.js (UMD and standalone) or croner.min.mjs (ES-module) from the dist/ folder

CDN

To use as a UMD-module (stand alone, RequireJS etc.)

<script src="https://cdn.jsdelivr.net/npm/croner@4/dist/croner.min.js"></script>

To use as a ES-module

<script type="module">
    import Cron from "https://cdn.jsdelivr.net/npm/croner@4/dist/croner.min.mjs";

    // ... see usage section ...
</script>

Documentation

Full documentation available at hexagon.github.io/croner.

The short version:

Signature

Cron takes three arguments

• pattern
• options (optional)
• scheduled function (optional)

const job = Cron("* * * * * *" /* Or a date object, or ISO 8601 local time */ , /*optional*/ { maxRuns: 1 } , /*optional*/ () => {} );

// If function is omitted in constructor, it can be scheduled later
job.schedule((/* optional */ job, /* optional */ context) => {});		

// States
const nextRun = job.next( /*optional*/ previousRun );	// Get a Date object representing next run
const nextRuns = job.enumerate(10, /*optional*/ startFrom ); // Get a array of Dates, containing next 10 runs according to pattern
const prevRun = job.previous( );	
const msToNext = job.msToNext( /*optional*/ previousRun ); // Milliseconds left to next execution
const isRunning = job.running();

// Control scheduled execution
job.pause();				
job.resume();
job.stop();

Options

Pattern

The expressions of Croner are very similar to the ones of Vixie Cron, with a few additions and changes listed below.

• In croner, a combination of day-of-week and day-of-month will only trigger when both conditions match. An example: 0 20 1 * MON will only trigger when monday occur the first day of any month. In Vixie Cron, it would trigger every monday AND the first day of every month. Vixie style can be enabled with legacyMode: true from version 4.2.0. See issue #53 for more information.

• Croner expressions support the following additional modifiers

  • ? A question mark is substituted with croner initialization time, as an example - ? ? * * * * would be substituted with 25 8 * * * * if time is <any hour>:08:25 at the time of new Cron('? ? * * * *', <...>). The question mark can be used in any field.
  • L L can be used in the day of month field, to specify the last day of the month.

• Croner also allow you to pass a javascript Date object, or a ISO 8601 formatted string, as a pattern. The scheduled function will trigger once at the specified date/time. If you use a timezone different from local, you pass ISO 8601 local time in target location, and specify timezone using the options (2nd parameter).

// ┌──────────────── (optional) second (0 - 59)
// │ ┌────────────── minute (0 - 59)
// │ │ ┌──────────── hour (0 - 23)
// │ │ │ ┌────────── day of month (1 - 31)
// │ │ │ │ ┌──────── month (1 - 12, JAN-DEC)
// │ │ │ │ │ ┌────── day of week (0 - 6, SUN-Mon) 
// │ │ │ │ │ │       (0 to 6 are Sunday to Saturday; 7 is Sunday, the same as 0)
// │ │ │ │ │ │
// * * * * * *

Note: Weekday and month names are case insensitive. Both MON and mon works.

Examples

Expressions

// Run a function according to pattern
Cron('15-45/10 */5 1,2,3 ? JAN-MAR SAT', function () {
    console.log('This will run every tenth second between second 15-45');
    console.log('every fifth minute of hour 1,2 and 3 when day of month');
    console.log('is the same as when Cron started, every saturday in January to March.');
});

Find dates

// Find next month
const nextMonth = Cron("0 0 0 1 * *").next(),
    nextSunday = Cron("0 0 0 * * 7").next(),
    nextSat29feb = Cron("0 0 0 29 2 6").next(),
    nextSunLastOfMonth = Cron("0 0 0 L * 7").next();

console.log("First day of next month: " +  nextMonth.toLocaleDateString());
console.log("Next sunday: " +  nextSunday.toLocaleDateString());
console.log("Next saturday at 29th of february: " +  nextSat29feb.toLocaleDateString());  // 2048-02-29
console.log("Next month ending with a sunday: " +  nextSunLastOfMonth.toLocaleDateString()); 

With options

const job = Cron(
    '* * * * *', 
    { 
        maxRuns: Infinity, 
        startAt: "2021-11-01T00:00:00", 
        stopAt: "2021-12-01T00:00:00",
        timezone: "Europe/Stockholm"
    },
    function() {
        console.log('This will run every minute, from 2021-11-01 to 2021-12-01 00:00:00');
    }
);

Job controls

const job = Cron('* * * * * *', (self) => {
    console.log('This will run every second. Pause on second 10. Resume on 15. And quit on 20.');
    console.log('Current second: ', new Date().getSeconds());
    console.log('Previous run: ' + self.previous());
    console.log('Next run: ' + self.next());
});

Cron('10 * * * * *', {maxRuns: 1}, () => job.pause());
Cron('15 * * * * *', {maxRuns: 1}, () => job.resume());
Cron('20 * * * * *', {maxRuns: 1}, () => job.stop());

Passing a context

const data = {
    what: "stuff"
};

Cron('* * * * * *', { context: data }, (_self, context) => {
    console.log('This will print stuff: ' + context.what);
});

Cron('*/5 * * * * *', { context: data }, (self, context) => {
    console.log('After this, other stuff will be printed instead');
    context.what = "other stuff";
    self.stop();
});

Fire on a specific date/time

// A javascript date, or a ISO 8601 local time string can be passed, to fire a function once. 
// Always specify which timezone the ISO 8601 time string has with the timezone option.
let job = Cron("2025-01-01T23:00:00",{timezone: "Europe/Stockholm"},() => {
    console.log('This will run at 2025-01-01 23:00:00 in timezone Europe/Stockholm');
});

if (job.next() === null) {
    // The job will not fire for some reason
} else {
    console.log("Job will fire at " + job.next());
}

Contributing

See Contribution Guide

License

MIT