cRonstrue

cRonstrue is a JavaScript library that parses a cron expression and outputs a human readable description of the cron schedule. For example, given the expression "*/5 * * * *" it will output "Every 5 minutes".

This library was ported from the original C# implemenation called cron-expression-descriptor and is also available in a few other languages.

Features

• Zero dependencies
• Supports all cron expression special characters including * / , - ? L W, #
• Supports 5, 6 (w/ seconds or year), or 7 (w/ seconds and year) part cron expressions
• Supports Quartz Job Scheduler cron expressions
• i18n support with 26 languages

Demo

A demo is available here.

Installation

cRonstrue is exported as an UMD module so it will work in an AMD, CommonJS or browser global context.

First, install the module:

npm install cronstrue

Then, depending upon your usage context, add a reference to it:

Node

var cronstrue = require('cronstrue');

ESM / webpack / TypeScript

import cronstrue from 'cronstrue';

Browser

The cronstrue.min.js file from the /dist folder in the npm package should be served to the browser. There are no dependencies so you can simply include the library in a <script> tag.

<script src="cronstrue.min.js" type="text/javascript"></script>
<script>
  var cronstrue = window.cronstrue;
</script>

CDN

A simple way to load the library in a browser is by using the unpkg CDN, which is a "fast, global content delivery network for everything on npm". To use it, include a script tag like this in your file:

<script src="https://unpkg.com/cronstrue@latest/dist/cronstrue.min.js" async></script>

Using the "latest" tag will result in a 302 redirect to the latest version tag so it is highly recommended to use a specific version tag such as https://unpkg.com/[email protected]/dist/cronstrue.min.js to avoid this redirect.

Usage

cronstrue.toString("* * * * *");
> "Every minute"

cronstrue.toString("0 23 ? * MON-FRI");
> "At 11:00 PM, Monday through Friday"

cronstrue.toString("0 23 * * *", { verbose: true });
> "At 11:00 PM, every day"

cronstrue.toString("23 12 * * SUN#2");
> "At 12:23 PM, on the second Sunday of the month"

cronstrue.toString("23 14 * * SUN#2", { use24HourTimeFormat: true });
> "At 14:23, on the second Sunday of the month"

cronstrue.toString("* * * ? * 2-6/2", { dayOfWeekStartIndexZero: false });
> "Every second, every 2 days of the week, Monday through Friday"

For more usage examples, including a demonstration of how cRonstrue can handle some very complex cron expressions, you can reference the unit tests.

Options

An options object can be passed as the second parameter to cronstrue.toString. The following options are available:

• throwExceptionOnParseError: boolean - If exception occurs when trying to parse expression and generate description, whether to throw or catch and output the Exception message as the description. (Default: true)
• verbose: boolean - Whether to use a verbose description (Default: false)
• dayOfWeekStartIndexZero: boolean - Whether to interpret cron expression DOW 1 as Sunday or Monday. (Default: true)
• use24HourTimeFormat: boolean - If true, descriptions will use a 24-hour clock (Default: false but some translations will default to true)
• locale: string - The locale to use (Default: "en")

i18n

To use the i18n support cRonstrue provides, you must use the packaged library that contains the locale transalations. Once you do this, you can pass the name of a supported locale as an option to cronstrue.toString(). For example, for the es (Spanish) locale, you would use: cronstrue.toString("* * * * *", { locale: "es" });.

Node

var cronstrue = require('cronstrue/i18n');
cronstrue.toString("*/5 * * * *", { locale: "fr" });

Browser

The cronstrue-i18n.min.js file from the /dist folder in the npm package should be served to the browser.

<script src="cronstrue-i18n.min.js" type="text/javascript"></script>
<script>
  cronstrue.toString("*/5 * * * *", { locale: "fr" });
</script>

Frequently Asked Questions

The cron expression I am passing in is not valid and this library is giving strange output. What should I do?

This library does not do full validation of cron expressions and assumes the expression passed in is valid. If you need to validate an expression consider using a library like cron-validator or cron-parser.

Can cRonstrue output the next occurrence of the cron expression?

No, cRonstrue does not support this. It simply describes a cron expression. You could use another library to get the next occurance of a cron expression and then pass that expression into cRonstrue, to acheive this.

Supported Locales

• en - English
• ca - Catalan
• cs - Czech
• es - Spanish
• da - Danish
• de - German
• fi - Finnish
• fr - French
• fa - Farsi
• he - Hebrew
• it - Italian
• ja - Japanese
• ko - Korean
• nb - Norwegian
• nl - Dutch
• pl - Polish
• pt_BR - Portuguese (Brazil)
• ro - Romanian
• ru - Russian
• sk - Slovakian
• sl - Slovenian
• sw - Swahili
• sv - Swedish
• tr - Turkish
• uk - Ukrainian
• zh_CN - Chinese (Simplified)
• zh_TW - Chinese (Traditional)

License

cRonstrue is freely distributable under the terms of the MIT license.