cronr ·

Inspired from unix cron, cronr is served as an time-based job scheduler which runs on browser and Node.js. It follows the basic standard macro pattern and makes somehow enhancement.

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Feature

• More time control support, even to millisecond
• Works on browser and Node.js
• By default, jobs control support five available actions : start, stop, stop, resume and clear.
• Standalone module to help calculate nextTick only, which provide a Iterator object to fetch.
• Add webWorkers support, to avoid the onmessage handle trigger delay due to the nature of Javascript's single thread.

Online demo

Cronr stroies -- online samples

Installation

• use npm to install

npm install cronr

• or use yarn with

yarn add cronr

Running on browser

• Downloading the Cronr.umd.min.js(for time job scheduler) or CronrCounter.umd.min.js(to fetch the nextTick only) from './lib/minified';
• Add an <script> tag which includes the bundle file on your page
• Refer to Cronr or CronrCounter for usage detail

Cronr

Job scheduler, which support cron macro pattern and has lots of handful methods.

- Cronr(pattern: string, callback: function, opts: obj)

| Property | Description | Type | Required| | -------- | --- -------- | ---- | --- | | pattern | cron macro format string | string | yes| | callback | Function will be triggerd when time hit nextTick | function | yes|

opts has following available parameters

Property	Description	Type	Required	Default
startTime	Starting point, when to start calculate the nextTick	Date	false	new Date()
endTime	Ending point, the schedulerd jobs will be canceled after this time	Date	false	none
immediate	When to trigger callback immediately when you start the job	boolean	false	false

methods

Method	Description	Signature
start	Start the initial job	(): void => {}
stop	Suspend the running job	(): void => {}
resume	Resume the suspend job	(): void => {}
clear	Clear the job	(): void => {}
restart	Restart the register job	(): void => {}

However, every method invoke has an order restriction.

• start only could be followed by stop and clear method.

Method	Followed By
start	["stop", "clear"]
stop	["resume", "clear"]
clear	["restart"]

Basic Usage

import Cronr from 'cronr';
// trigger on every second, 10, 20, 30, 40, 50, 00
const pattern = '*/10 * * * * *';
let count = 1;
const cb = () => count++;
 
const job = new Cronr(pattern, cb, {
    startTime: new Date(2018, 3, 23, 10, 23, 36),
});
 
job.start();

CronrCounter

It mainly consists of :

• Parsing cron macro pattern
• A Iterator property which to provide the nextTick value.

- CronrCounter(opts: obj)

opts has the following avaible properties.

Property	Description	Type	Required	Default
name	Module name	string	false	undefined
pattern	cron macro pattern	string	true	--
ts	Time Starting point, which means all the nextTick is calculated based on this value	Date	false	new Date()

- Basic Usage

import CronrCounter from 'cronr/CronrCounter';
const counter = new CronrCounter({
  name: 'testing',
  pattern: '2,5 * * 3-12 3 *',
  ts: new Date(2018, 7, 22, 10, 23, 16),
});
 
const data = counter.result;
const result = data.next().value;  // '3/3/2019, 12:00:02 AM'
const result2 = data.next().value; // '3/3/2019, 12:00:05 AM'

CronrWorker

This is an experimental feature which is integrated with webWorkers. It coulb be considered as an alternate of Crorn module。

Why using webWorkers

let i = 1;
const fn = (ts) => {
  const id = setTimeout(() => {
    const executedAt = new Date();
    const diff = executedAt - ts;
    window.clearTimeout(id);
    console.log('executedAt ', executedAt, diff);
    if (i < 10) {
      fn(ts);
    }
    i++;
  }, 500)
}
 
// result
 
// executedAt  Mon May 07 2018 00:33:38 GMT+0800 (CST) 502
// executedAt  Mon May 07 2018 00:33:38 GMT+0800 (CST) 1007
// executedAt  Mon May 07 2018 00:33:39 GMT+0800 (CST) 1509
// executedAt  Mon May 07 2018 00:33:39 GMT+0800 (CST) 2015
// executedAt  Mon May 07 2018 00:33:40 GMT+0800 (CST) 2521
// executedAt  Mon May 07 2018 00:33:40 GMT+0800 (CST) 3027
// executedAt  Mon May 07 2018 00:33:41 GMT+0800 (CST) 3529
// executedAt  Mon May 07 2018 00:33:41 GMT+0800 (CST) 4037
// executedAt  Mon May 07 2018 00:33:42 GMT+0800 (CST) 4538
// executedAt  Mon May 07 2018 00:33:42 GMT+0800 (CST) 5040
// executedAt  Mon May 07 2018 00:33:43 GMT+0800 (CST) 5546
// executedAt  Mon May 07 2018 00:33:43 GMT+0800 (CST) 6052
// executedAt  Mon May 07 2018 00:33:44 GMT+0800 (CST) 6555
// executedAt  Mon May 07 2018 00:33:44 GMT+0800 (CST) 7059
// executedAt  Mon May 07 2018 00:33:45 GMT+0800 (CST) 7564
// executedAt  Mon May 07 2018 00:33:45 GMT+0800 (CST) 8068
// executedAt  Mon May 07 2018 00:33:46 GMT+0800 (CST) 8573
// executedAt  Mon May 07 2018 00:33:46 GMT+0800 (CST) 9080
// executedAt  Mon May 07 2018 00:33:47 GMT+0800 (CST) 9586
// executedAt  Mon May 07 2018 00:33:47 GMT+0800 (CST) 10092

According to the running result, As the counter become bigger, the delay will become much bigger. For example, if count === 10, the delay is only 40ms, but when the count is 20, it become 92. It is due to the nature of Javascript's single thread, setTimeout jobs could not running on concurrency. instead, they could be blockded if the main thread is busy on other things.

webWorkers provide a method to do a single job in a seperate thread. This job will not be affected by main thread's blocking. Then it also has a hand-on method postMessage to communiate with main thread.

-CronrWorker(pattern: string)

Property	Description	Type	Required
pattern	cron macro format string	string	yes

Basic CronrWorker Usage

import CronrWorker from 'cronr/CronrWorker'
 
const worker = CronrWorker(pattern);
worker.onmessage = (e) => {
  const data = e.data;
  const { nextTick, triggerAt, hit, status, action } = data;
 
  if (action === 'trigger') {
    this.store.set(hit, {
      triggerAt,
      nextTick,
    });
    this.setState({
      count: this.state.count + 1,
      status,
    });
  }
 
  if (action === 'updateStatus') {
    this.setState({
      status,
    });
  }
};
 
worker.onerror = (e) => {
  const { message } = e;
  console.log(e.message);
};

Cronr Macro Pattern

It mainly inspired from Cron - Wikipedia. Comparing with original format, it follows the basic syntax; For example, Every pattern is seperated by space; It still support special meaning characters(-, , and * etc);

However, it has addtional enhancement. Recently, it support time format till milliseconds. Just as follows showing.

*   *   *   *   *   *   *
┬   ┬   ┬   ┬   ┬   ┬   ┬
|   |   |   |   |   |   |
|   |   |   |   |   |   |_________  day of week (0 - 6)
|   |   |   |   |   |_____________  month (1 - 12)
|   |   |   |   |_________________  day of month (1 - 31)
|   |   |   |_____________________  hour (0 - 23)
|   |   |_________________________  minute (0 - 59)
|   |_____________________________  second (0 - 59, optional)
|_________________________________  milliSecond (0 - 999, optional)

How to write an valid macro pattern

You must provide a string which combines with at least 5 valid macro token(* or 1,2,4-5 will be considered as a token); It means if the token length is less than 7, it will has an auto-completion on the heading position.

const patten = '* * 5 * * * *'   // retain the same
const pattern = '5 * * * *';     // => '* * 5 * * * *'
const pattern2 = '5 * * * * *';  // => '* 5 * * * * *'

Simple macro samples

• Pay attention to the token length

'* * * * * * *'       // running on every millisecond
 
'*/10 * * * * *'      // running on every 10 seconds
 
'30 4 1,15 * 5'       // run at 4:30 am on the 1st and 15th of each month, plus every Friday
 
'15 14 1 * *'         // run at 2:15pm on the first of every month
 
'5 4 * * sun'         // run at 5 after 4 every sunday

if both "day of month" and "day of week" are restricted (not "*"), then one or both must match the current day.

Todo

Nonstandard predefined scheduling definitions

To support preset macro pattern, such as @yearly which means run once a year at midnight of 1 Jan.

Futher Reading for Cron Macro

Online tools to simulate cron pattern

• Free Online Cron Expression Generator and Describer - FreeFormatter.com

• Describes Cron expressions as human readable text

Wikis

• Cron - Wikipedia
• crontab(5)