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2.6.4 • Public • Published


Library for working with recurrence rules for calendar dates.

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rrule.js supports recurrence rules as defined in the iCalendar RFC, with a few important differences. It is a partial port of the rrule module from the excellent python-dateutil library. On top of that, it supports parsing and serialization of recurrence rules from and to natural language.

Quick Start

Client Side

$ yarn add rrule

Alternatively, download manually:

<script src="rrule/dist/es5/rrule.min.js"></script>

Server Side

Includes optional TypeScript types

$ yarn add rrule
# or 
$ npm install rrule



import { RRule, RRuleSet, rrulestr } from 'rrule'
// Create a rule:
const rule = new RRule({
  freq: RRule.WEEKLY,
  interval: 5,
  byweekday: [RRule.MO, RRule.FR],
  dtstart: new Date(Date.UTC(2012, 1, 1, 10, 30)),
  until: new Date(Date.UTC(2012, 12, 31))
// Get all occurrence dates (Date instances):
[ '2012-02-03T10:30:00.000Z',
 /* … */]
// Get a slice:
rule.between(new Date(Date.UTC(2012, 7, 1)), new Date(Date.UTC(2012, 8, 1)))
// Get an iCalendar RRULE string representation:
// The output can be used with RRule.fromString().
// Get a human-friendly text representation:
// The output can be used with RRule.fromText().
"every 5 weeks on Monday, Friday until January 31, 2013"


const rruleSet = new RRuleSet()
// Add a rrule to rruleSet
rruleSet.rrule(new RRule({
  freq: RRule.MONTHLY,
  count: 5,
  dtstart: new Date(Date.UTC(2012, 1, 1, 10, 30))
// Add a date to rruleSet
rruleSet.rdate(new Date(Date.UTC(2012, 6, 1, 10, 30)))
// Add another date to rruleSet
rruleSet.rdate(new Date(Date.UTC(2012, 6, 2, 10, 30)))
// Add a exclusion rrule to rruleSet
rruleSet.exrule(new r.RRule({
  freq: RRule.MONTHLY,
  count: 2,
  dtstart: new Date(Date.UTC(2012, 2, 1, 10, 30))
// Add a exclusion date to rruleSet
rruleSet.exdate(new Date(Date.UTC(2012, 5, 1, 10, 30)))
// Get all occurrence dates (Date instances):
[ '2012-02-01T10:30:00.000Z',
  '2012-07-02T10:30:00.000Z' ]
// Get a slice:
rruleSet.between(new Date(Date.UTC(2012, 2, 1)), new Date(Date.UTC(2012, 6, 2)))
[ '2012-05-01T10:30:00.000Z', '2012-07-01T10:30:00.000Z' ]
 // To string
// To string


// Parse a RRule string, return a RRule object
// Parse a RRule string, return a RRuleSet object
rrulestr('DTSTART:20120201T023000Z\nRRULE:FREQ=MONTHLY;COUNT=5', {forceset: true})
// Parse a RRuleSet string, return a RRuleSet object

Important: Use UTC dates

Dates in JavaScript are tricky. RRule tries to support as much flexibility as possible without adding any large required 3rd party dependencies, but that means we also have some special rules.

By default, RRule deals in "floating" times or UTC timezones. If you want results in a specific timezone, RRule also provides timezone support. Either way, JavaScript's built-in "timezone" offset tends to just get in the way, so this library simply doesn't use it at all. All times are returned with zero offset, as though it didn't exist in JavaScript.

The bottom line is the returned "UTC" dates are always meant to be interpreted as dates in your local timezone. This may mean you have to do additional conversion to get the "correct" local time with offset applied.

For this reason, it is highly recommended to use timestamps in UTC eg. new Date(Date.UTC(...)). Returned dates will likewise be in UTC (except on Chrome, which always returns dates with a timezone offset).

For example:

// local machine zone is America/Los_Angeles
const rule = RRule.fromString(
[ 2018-11-01T18:00:00.000Z,
  2018-11-07T18:00:00.000Z ]
// Even though the given offset is `Z` (UTC), these are local times, not UTC times.
// Each of these this is the correct local Pacific time of each recurrence in
// America/Los_Angeles when it is 19:00 in America/Denver, including the DST shift.
// You can get the local components by using the getUTC* methods eg:
date.getUTCDate() // --> 1
date.getUTCHours() // --> 18

If you want to get the same times in true UTC, you may do so eg. using Luxon:

rule.all().map(date =>
  .setZone('local', { keepLocalTime: true })
[ 2018-11-02T01:00:00.000Z,
  2018-11-08T02:00:00.000Z ]
// These times are in true UTC; you can see the hours shift

For more examples see python-dateutil documentation.

Timezone Support

Optionally, it also supports use of the TZID parameter in the RFC when the Luxon library is provided. The specification and support matrix for Luxon apply.

Example with TZID:

new RRule({
  dtstart: new Date(Date.UTC(2018, 1, 1, 10, 30)),
  count: 1,
  tzid: 'Asia/Tokyo'
// assuming the system timezone is set to America/Los_Angeles, you get:
[ '2018-01-31T17:30:00.000Z' ]
// which is the time in Los Angeles when it's 2018-02-01T10:30:00 in Tokyo.

Whether or not you use the TZID param, make sure to only use JS Date objects that are represented in UTC to avoid unexpected timezone offsets being applied, for example:

// WRONG: Will produce dates with TZ offsets added
new RRule({
  freq: RRule.MONTHLY,
  dtstart: new Date(2018, 1, 1, 10, 30),
  until: new Date(2018, 2, 31)
[ '2018-02-01T18:30:00.000Z' ]
// RIGHT: Will produce dates with recurrences at the correct time
new RRule({
  freq: RRule.MONTHLY,
  dtstart: new Date(Date.UTC(2018, 1, 1, 10, 30)),
  until: new Date(Date.UTC(2018, 2, 31))
[ '2018-02-01T10:30:00.000Z' ]


RRule Constructor

new RRule(options[, noCache=false])

The options argument mostly corresponds to the properties defined for RRULE in the iCalendar RFC. Only freq is required.

Option Description

(required) One of the following constants:

  • RRule.YEARLY
  • RRule.WEEKLY
  • RRule.DAILY
  • RRule.HOURLY
dtstart The recurrence start. Besides being the base for the recurrence, missing parameters in the final recurrence instances will also be extracted from this date. If not given, new Date will be used instead. **IMPORTANT:** See the discussion under timezone support
interval The interval between each freq iteration. For example, when using RRule.YEARLY, an interval of 2 means once every two years, but with RRule.HOURLY, it means once every two hours. The default interval is 1.
wkst The week start day. Must be one of the RRule.MO, RRule.TU, RRule.WE constants, or an integer, specifying the first day of the week. This will affect recurrences based on weekly periods. The default week start is RRule.MO.
count How many occurrences will be generated.
until If given, this must be a Date instance, that will specify the limit of the recurrence. If a recurrence instance happens to be the same as the Date instance given in the until argument, this will be the last occurrence.
tzid If given, this must be a string supported by Luxon, and the Luxon library must be provided. See discussion under Timezone support.
bysetpos If given, it must be either an integer, or an array of integers, positive or negative. Each given integer will specify an occurrence number, corresponding to the nth occurrence of the rule inside the frequency period. For example, a bysetpos of -1 if combined with a RRule.MONTHLY frequency, and a byweekday of (RRule.MO, RRule.TU, RRule.WE, RRule.TH, RRule.FR), will result in the last work day of every month.
bymonth If given, it must be either an integer, or an array of integers, meaning the months to apply the recurrence to.
bymonthday If given, it must be either an integer, or an array of integers, meaning the month days to apply the recurrence to.
byyearday If given, it must be either an integer, or an array of integers, meaning the year days to apply the recurrence to.
byweekno If given, it must be either an integer, or an array of integers, meaning the week numbers to apply the recurrence to. Week numbers have the meaning described in ISO8601, that is, the first week of the year is that containing at least four days of the new year.
byweekday If given, it must be either an integer (0 == RRule.MO), an array of integers, one of the weekday constants (RRule.MO, RRule.TU, etc), or an array of these constants. When given, these variables will define the weekdays where the recurrence will be applied. It's also possible to use an argument n for the weekday instances, which will mean the nth occurrence of this weekday in the period. For example, with RRule.MONTHLY, or with RRule.YEARLY and BYMONTH, using RRule.FR.nth(+1) or RRule.FR.nth(-1) in byweekday will specify the first or last friday of the month where the recurrence happens. Notice that the RFC documentation, this is specified as BYDAY, but was renamed to avoid the ambiguity of that argument.
byhour If given, it must be either an integer, or an array of integers, meaning the hours to apply the recurrence to.
byminute If given, it must be either an integer, or an array of integers, meaning the minutes to apply the recurrence to.
bysecond If given, it must be either an integer, or an array of integers, meaning the seconds to apply the recurrence to.
byeaster This is an extension to the RFC specification which the Python implementation provides. Not implemented in the JavaScript version.

noCache: Set to true to disable caching of results. If you will use the same rrule instance multiple times, enabling caching will improve the performance considerably. Enabled by default.

See also python-dateutil documentation.

Instance properties

Processed options applied to the rule. Includes default options (such us wkstart). Currently, rule.options.byweekday isn't equal to rule.origOptions.byweekday (which is an inconsistency).
The original options argument passed to the constructor.

Occurrence Retrieval Methods


Returns all dates matching the rule. It is a replacement for the iterator protocol this class implements in the Python version.

As rules without until or count represent infinite date series, you can optionally pass iterator, which is a function that is called for each date matched by the rule. It gets two parameters date (the Date instance being added), and i (zero-indexed position of date in the result). Dates are being added to the result as long as the iterator returns true. If a false-y value is returned, date isn't added to the result and the iteration is interrupted (possibly prematurely).

[ '2012-02-01T10:30:00.000Z',
  '2012-07-02T10:30:00.000Z' ]
rule.all(function (date, i){return i < 2})
[ '2012-02-01T10:30:00.000Z',
  '2012-05-01T10:30:00.000Z' ]
RRule.prototype.between(after, before, inc=false [, iterator])

Returns all the occurrences of the rrule between after and before. The inc keyword defines what happens if after and/or before are themselves occurrences. With inc == true, they will be included in the list, if they are found in the recurrence set.

Optional iterator has the same function as it has with RRule.prototype.all().

rule.between(new Date(Date.UTC(2012, 7, 1)), new Date(Date.UTC(2012, 8, 1)))
RRule.prototype.before(dt, inc=false)

Returns the last recurrence before the given Date instance. The inc argument defines what happens if dt is an occurrence. With inc == true, if dt itself is an occurrence, it will be returned.

RRule.prototype.after(dt, inc=false)

Returns the first recurrence after the given Date instance. The inc argument defines what happens if dt is an occurrence. With inc == true, if dt itself is an occurrence, it will be returned.

See also python-dateutil documentation.

iCalendar RFC String Methods


Returns a string representation of the rule as per the iCalendar RFC. Only properties explicitly specified in options are included:

rule.toString() == RRule.optionsToString(rule.origOptions)

Converts options to iCalendar RFC RRULE string:

// Get full a string representation of all options,
// including the default and inferred ones.
// Cherry-pick only some options from an rrule:
  freq: rule.options.freq,
  dtstart: rule.options.dtstart

Constructs an RRule instance from a complete rfcString:

var rule = RRule.fromString("DTSTART:20120201T093000Z\nRRULE:FREQ=WEEKLY;")
// This is equivalent
var rule = new RRule(RRule.parseString("DTSTART:20120201T093000Z\nRRULE:FREQ=WEEKLY"))

Only parse RFC string and return options.

var options = RRule.parseString('FREQ=DAILY;INTERVAL=6')
options.dtstart = new Date(Date.UTC(2000, 1, 1))
var rule = new RRule(options)

Natural Language Text Methods

These methods provide an incomplete support for text–RRule and RRule–text conversion. You should test them with your input to see whether the result is acceptable.

RRule.prototype.toText([gettext, [language]])

Returns a textual representation of rule. The gettext callback, if provided, will be called for each text token and its return value used instead. The optional language argument is a language definition to be used (defaults to rrule/nlp.js:ENGLISH).

var rule = new RRule({
  freq: RRule.WEEKLY,
  count: 23
"every week for 23 times"

Provides a hint on whether all the options the rule has are convertible to text.

RRule.fromText(text[, language])

Constructs an RRule instance from text.

rule = RRule.fromText('every day for 3 times')
RRule.parseText(text[, language])

Parse text into options:

options = RRule.parseText('every day for 3 times')
// {freq: 3, count: "3"}
options.dtstart = new Date(Date.UTC(2000, 1, 1))
var rule = new RRule(options)

RRuleSet Constructor

new RRuleSet([noCache=false])

The RRuleSet instance allows more complex recurrence setups, mixing multiple rules, dates, exclusion rules, and exclusion dates.

Default noCache argument is false, caching of results will be enabled, improving performance of multiple queries considerably.


Include the given rrule instance in the recurrence set generation.


Include the given datetime instance in the recurrence set generation.


Include the given rrule instance in the recurrence set exclusion list. Dates which are part of the given recurrence rules will not be generated, even if some inclusive rrule or rdate matches them. NOTE: EXRULE has been (deprecated in RFC 5545)[] and does not support a DTSTART property.


Include the given datetime instance in the recurrence set exclusion list. Dates included that way will not be generated, even if some inclusive rrule or rdate matches them.


Sets or overrides the timezone identifier. Useful if there are no rrules in this RRuleSet and thus no DTSTART.


Same as RRule.prototype.all.

RRuleSet.prototype.between(after, before, inc=false [, iterator])

Same as RRule.prototype.between.

RRuleSet.prototype.before(dt, inc=false)

Same as RRule.prototype.before.

RRuleSet.prototype.after(dt, inc=false)

Same as RRule.prototype.after.


Get list of included rrules in this recurrence set.


Get list of excluded rrules in this recurrence set.


Get list of included datetimes in this recurrence set.


Get list of excluded datetimes in this recurrence set.

rrulestr Function

rrulestr(rruleStr[, options])

The rrulestr function is a parser for RFC-like syntaxes. The string passed as parameter may be a multiple line string, a single line string, or just the RRULE property value.

Additionally, it accepts the following keyword arguments:

cache If True, the rruleset or rrule created instance will cache its results. Default is not to cache.

dtstart If given, it must be a datetime instance that will be used when no DTSTART property is found in the parsed string. If it is not given, and the property is not found, will be used instead.

unfold If set to True, lines will be unfolded following the RFC specification. It defaults to False, meaning that spaces before every line will be stripped.

forceset If set to True a rruleset instance will be returned, even if only a single rule is found. The default is to return an rrule if possible, and an rruleset if necessary.

compatible If set to True, the parser will operate in RFC-compatible mode. Right now it means that unfold will be turned on, and if a DTSTART is found, it will be considered the first recurrence instance, as documented in the RFC.

tzid If given, it must be a string that will be used when no TZID property is found in the parsed string. If it is not given, and the property is not found, 'UTC' will be used by default.

Differences From iCalendar RFC

  • RRule has no byday keyword. The equivalent keyword has been replaced by the byweekday keyword, to remove the ambiguity present in the original keyword.
  • Unlike documented in the RFC, the starting datetime, dtstart, is not the first recurrence instance, unless it does fit in the specified rules. This is in part due to this project being a port of python-dateutil, which has the same non-compliant functionality. Note that you can get the original behavior by using a RRuleSet and adding the dtstart as an rdate.
var rruleSet = new RRuleSet()
var start = new Date(Date.UTC(2012, 1, 1, 10, 30))
// Add a rrule to rruleSet
rruleSet.rrule(new RRule({
  freq: RRule.MONTHLY,
  count: 5,
  dtstart: start
// Add a date to rruleSet
  • Unlike documented in the RFC, every keyword is valid on every frequency (the RFC documents that byweekno is only valid on yearly frequencies, for example).


rrule.js is implemented in Typescript. It uses JavaScript Standard Style coding style.

To run the code, checkout this repository and run:

$ yarn

To run the tests, run:

$ yarn test

To build files for distribution, run:

$ yarn build


Python dateutil is written by Gustavo Niemeyer.

See LICENCE for more details.

Related projects

  • — RESTful API to get back occurrences of RRULEs that conform to RFC 5545.


npm i rrule

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