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https://github.com/wanasit/chrono

A natural language date parser in Javascript
https://github.com/wanasit/chrono

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A natural language date parser in Javascript

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# Chrono (v2)



A natural language date parser in Javascript. 



![Build Status](https://github.com/github/docs/actions/workflows/test.yml/badge.svg)

[![Coverage Status](https://img.shields.io/coverallsCoverage/github/wanasit/chrono.svg)](https://coveralls.io/r/wanasit/chrono?branch=master)



It is designed to handle most date/time format and extract information from any given text:



* _Today_, _Tomorrow_, _Yesterday_, _Last Friday_, etc

* _17 August 2013 - 19 August 2013_

* _This Friday from 13:00 - 16.00_

* _5 days ago_

* _2 weeks from now_

* _Sat Aug 17 2013 18:40:39 GMT+0900 (JST)_

* _2014-11-30T08:15:30-05:30_



### Installation



With npm:

```bash

$ npm install --save chrono-node

```

    

```javascript

import * as chrono from 'chrono-node';



chrono.parseDate('An appointment on Sep 12-13'); 

```

For Node.js:

```javascript

const chrono = require('chrono-node');



// or `import chrono from 'chrono-node'` for ECMAScript

```



### What's changed in the v2

For Users

* Chrono’s default now handles only international English. While in the previous version, it tried to parse with all known languages.

* The current fully supported languages are `en`, `ja`, `fr`, `nl`, `ru` and `uk` (`de`, `pt`, and `zh.hant` are partially supported). 



For contributors and advanced users

* The project is rewritten in TypeScript

* New [Parser](#parser) and [Refiner](#refiner) interface 

* New source code structure. All parsers, refiners, and configuration should be under a locale directory (See. `locales/en`)



**Note: [v1.x.x](https://github.com/wanasit/chrono/tree/v1.x.x) will still be supported for the time being.**



## Usage



Simply pass a `string` to functions `chrono.parseDate` or `chrono.parse`. 



```javascript

import * as chrono from 'chrono-node';



chrono.parseDate('An appointment on Sep 12-13');

// Fri Sep 12 2014 12:00:00 GMT-0500 (CDT)

    

chrono.parse('An appointment on Sep 12-13');

/* [{ 

    index: 18,

    text: 'Sep 12-13',

    start: ...

}] */

```



For more advanced usage, here is the typescript definition of the `parse` function:

```typescript

parse(text: string, ref?: ParsingReference, option?: ParsingOption): ParsedResult[] {...}

```



#### Parsing Reference (Date / Timezone)



Today's "Friday" is different from last month's "Friday". 

The meaning of the referenced dates depends on when and where they are mentioned. 

Chrono lets you define the reference as `Date` or `ParsingReference` object:



```javascript

// (Note: the examples run on JST timezone)



chrono.parseDate('Friday', new Date(2012, 8 - 1, 23)); 

// Fri Aug 24 2012 12:00:00 GMT+0900 (JST)



chrono.parseDate('Friday', new Date(2012, 8 - 1, 1)); 

// Fri Aug 03 2012 12:00:00 GMT+0900 (JST)



chrono.parseDate("Friday at 4pm", {

    // Wed Jun 09 2021 21:00:00 GMT+0900 (JST)

    // = Wed Jun 09 2021 07:00:00 GMT-0500 (CDT)

    instant: new Date(1623240000000), 

    timezone: "CDT",

})

// Sat Jun 12 2021 06:00:00 GMT+0900 (JST)

// = Fri Jun 11 2021 16:00:00 GMT-0500 (CDT)

```



#### ParsingReference

* `instant?: Date` The instant when the input is written or mentioned

* `timezone?: string | number` The timezone where the input is written or mentioned. 

  Support minute-offset (number) and timezone name (e.g. "GMT", "CDT")



### Parsing Options



`forwardDate` (boolean) to assume the results should happen after the reference date (forward into the future)



```javascript

const referenceDate = new Date(2012, 7, 25);

// Sat Aug 25 2012 00:00:00 GMT+0900 -- The reference date was Saturday



chrono.parseDate('Friday', referenceDate);

// Fri Aug 24 2012 12:00:00 GMT+0900 (JST) -- The day before was Friday



chrono.parseDate('Friday', referenceDate, { forwardDate: true });

// Fri Aug 31 2012 12:00:00 GMT+0900 (JST) -- The following Friday

```



`timezones` Override or add custom mappings between timezone abbreviations and offsets. Use this when you want Chrono to parse certain text into a given timezone offset. Chrono supports both unambiguous (normal) timezone mappings and ambigous mappings where the offset is different during and outside of daylight savings.



```javascript

// Chrono doesn't understand XYZ, so no timezone is parsed

chrono.parse('at 10:00 XYZ', new Date(2023, 3, 20))

// "knownValues": {"hour": 10, "minute": 0}



// Make Chrono parse XYZ as offset GMT-0300 (180 minutes)

chrono.parse('at 10:00 XYZ', new Date(2023, 3, 20), { timezones: { XYZ: -180 } })

// "knownValues": {"hour": 10, "minute": 0, "timezoneOffset": -180}



// Make Chrono parse XYZ as offset GMT-0300 outside of DST, and GMT-0200 during DST. Assume DST is between 

import { getLastDayOfMonthTransition } from "timezone";

import { Weekday, Month } from "parsing";



const parseXYZAsAmbiguousTz = {

  timezoneOffsetDuringDst: -120,

  timezoneOffsetNonDst: -180,

  dstStart: (year: number) => getLastWeekdayOfMonth(year, Month.FEBRUARY, Weekday.SUNDAY, 2),

  dstEnd: (year: number) => getLastWeekdayOfMonth(year, Month.SEPTEMBER, Weekday.SUNDAY, 3)

};

// Parsing a date which falls within DST

chrono.parse('Jan 1st 2023 at 10:00 XYZ', new Date(2023, 3, 20), { timezones: { XYZ: parseXYZAsAmbiguousTz } })

// "knownValues": {"month": 1, ..., "timezoneOffset": -180}



// Parsing a non-DST date

chrono.parse('Jun 1st 2023 at 10:00 XYZ', new Date(2023, 3, 20), { timezones: { XYZ: parseXYZAsAmbiguousTz } })

// "knownValues": {"month": 6, ..., "timezoneOffset": -120}

```



### Parsed Results and Components



#### ParsedResult

* `refDate: Date` The [reference date](#reference-date) of this result

* `index: number` The location within the input text of this result  

* `text: string`  The text this result that appears in the input 

* `start: ParsedComponents` The parsed date components as a [ParsedComponents](#parsedcomponents) object

* `end?: ParsedComponents`  Similar to `start`

* `date: () => Date` Create a javascript Date



#### ParsedComponents

* `get: (c: Component) => number | null`    Get known or implied value for the component

* `isCertain: (c: Component) => boolean`    Check if the component has a known value

* `date: () => Date`    Create a javascript Date



For example:

```js

const results = chrono.parse('I have an appointment tomorrow from 10 to 11 AM');



results[0].index;     // 22

results[0].text;      // 'tomorrow from 10 to 11 AM'

results[0].refDate;   // Sat Dec 13 2014 21:50:14 GMT-0600 (CST)



// `start` is Sat Dec 14 2014 10:00:00

results[0].start.get('day');    // 14 (the 14th, the day after refDate)

results[0].start.get('month');  // 12 (or December)

results[0].start.get('hour');   // 10 

results[0].start.date();        // Sun Dec 14 2014 10:00:00 GMT-0600 (CST)



...

results[0].end.date();  // Sun Dec 14 2014 11:00:00 GMT-0600 (CST)

```



### Strict vs Casual configuration



Chrono comes with `strict` mode that parse only formal date patterns. 



```js

// 'strict' mode

chrono.strict.parseDate('Today');       // null

chrono.strict.parseDate('Friday');      // null

chrono.strict.parseDate('2016-07-01');  // Fri Jul 01 2016 12:00:00 ...

chrono.strict.parseDate('Jul 01 2016'); // Fri Jul 01 2016 12:00:00 ...



// 'casual' mode (default) 

chrono.parseDate('Today');              // Thu Jun 30 2016 12:00:00 ...

chrono.casual.parseDate('Friday');      // Fri Jul 01 2016 12:00:00 ...

chrono.casual.parseDate('2016-07-01');  // Fri Jul 01 2016 12:00:00 ...

chrono.casual.parseDate('Jul 01 2016'); // Fri Jul 01 2016 12:00:00 ...

```



### Locales



By default, Chrono is configured to handle **only international English**. 

This differs from the previous version of Chrono that would try all locales by default.



There are several locales supported contributed by multiple developers under `./locales` directory.



```js

// default English (US)

chrono.parseDate('6/10/2018');    



chrono.en.parseDate('6/10/2018');       // June 10th, 2018

chrono.en.GB.parseDate('6/10/2018');    // October 6th, 2018



chrono.ja.parseDate('昭和６４年１月７日'); 

```



Current supported locale options are: `en`, `ja`, `fr`, `nl`, `ru` and `uk` (`de`, `pt`, and `zh.hant` are partially supported).



#### Importing specific locales



Chrono exports all locale options by default for simplicity. However, this can cause issues when using Chrono if you're using a Node.js runtime that was built with the Intl module disabled (with the `--without-intl` flag), such as: 

```

Invalid regular expression: /* omitted */: Invalid property name in character class

```



This is because the Intl module is required to handle special characters, such as Cyrillic (`ru`).



To avoid this, you can specify only the locale(s) you want to import:

```typescript

// CommonJS (Node.js)

const chrono = require('chrono-node/en')



// ECMAScript

import chrono from 'chrono-node/en'



// TypeScript

// Warning: `moduleResolution` must be set to `node16` or `nodeNext` in tsconfig.json`

import * as chrono from 'chrono-node/en'

```



## Customize Chrono



Chrono’s extraction pipeline configuration consists of `parsers: Parser[]` and `refiners: Refiner[]`.



* First, each parser independently extracts patterns from input text input and create parsing results  ([ParsingResult](#parsedresult)).

* Then, the parsing results are combined, sorted, and refined with the refiners. In the refining phase, the results can be filtered-out, merged, or attached with additional information.



### Parser



```typescript

interface Parser {

    pattern: (context: ParsingContext) => RegExp,

    extract: (context: ParsingContext, match: RegExpMatchArray) =>

        (ParsingComponents | ParsingResult | {[c in Component]?: number} | null)

}

```



Parser is a module for low-level pattern-based parsing. 

Ideally, each parser should be designed to handle a single specific date format. 



User can create a new parser for supporting new date formats or languages

 by providing RegExp pattern `pattern()` and extracting result or components from the RegExp match `extract()`.



```javascript

const custom = chrono.casual.clone();

custom.parsers.push({

    pattern: () => { return /\bChristmas\b/i },

    extract: (context, match) => {

        return {

            day: 25, month: 12

        }

    }

});



custom.parseDate("I'll arrive at 2.30AM on Christmas night");

// Wed Dec 25 2013 02:30:00 GMT+0900 (JST)

// 'at 2.30AM on Christmas'

```



### Refiner



```typescript

interface Refiner {

    refine: (context: ParsingContext, results: ParsingResult[]) => ParsingResult[]

}

```



Refiner is a higher level module for improving or manipulating the results. User can add a new type of refiner to customize Chrono's results or to add some custom logic to Chrono.



```javascript

const custom = chrono.casual.clone();

custom.refiners.push({

    refine: (context, results) => {

        // If there is no AM/PM (meridiem) specified,

        //  let all time between 1:00 - 4:00 be PM (13.00 - 16.00)

        results.forEach((result) => {

            if (!result.start.isCertain('meridiem') &&

                result.start.get('hour') >= 1 && result.start.get('hour') < 4) {



                result.start.assign('meridiem', 1);

                result.start.assign('hour', result.start.get('hour') + 12);

            }

        });

        return results;

    }

});



// This will be parsed as PM.

// > Tue Dec 16 2014 14:30:00 GMT-0600 (CST) 

custom.parseDate("This is at 2.30");



// Unless the 'AM' part is specified

// > Tue Dec 16 2014 02:30:00 GMT-0600 (CST)

custom.parseDate("This is at 2.30 AM");

```



In the example, the custom refiner assigns PM to parsing results with ambiguous [meridiem](http://en.wikipedia.org/wiki/12-hour_clock). 

The `refine` method of the refiner class will be called with parsing [results](#parsedresult) (from [parsers](#parser) or other previous refiners). 

The method must return an array of the new results (which, in this case, we modified those results in place).



### More documentation



Checkout the Typescript Documentation in the project's [Github page](http://wanasit.github.io/chrono/).



## Development Guides



This guide explains how to set up chrono project for prospective contributors.



```bash

# Clone and install library

$ git clone https://github.com/wanasit/chrono.git chrono

$ cd chrono

$ npm install



```



Parsing date from text is complicated. A small change can have effects on unexpected places. 

So, Chrono is a heavily tested library. 

Commits that break a test shouldn't be allowed in any condition.



Chrono's unit testing is based-on [Jest](https://facebook.github.io/jest/). 



```bash

# Run the test

$ npm run test



# Run the test in watch mode

$ npm run watch

```



Chrono's source files is in `src` directory. 

The built bundle (`dist/*`) is created by running [Webpack](https://webpack.js.org/) via the following command 



```bash

$ npm run build

```