Temporal Expressions in Javascript

Introduction

Temporal expressions allow defining and querying recurring events on calendars. This little library roughly follows the ideas of Martin Fowler's article about recurring events.

Example: Races take place Wednesdays in summer (September until April, in the Southern Hemisphere) and Saturdays in winter (May until August).

var t = require('tempex');

var winterMonths = t.months([4, 5, 6, 7]); // we use Javascript convention: May=4, June=5, ...
var summerMonths = t.negate(winterMonths);
var raceSchedule = t.union([
  // summer
  t.intersectionOf(
    summerMonths,
    t.onWeekdays([ 3 ]) // Wednesday=3
  ),
  // winter
  t.intersectionOf(
    winterMonths,
    t.onWeekdays([ 6 ]) // Saturdays=6
  ),
])

To determine the actual occurrences (days) of this schedule in a time range:

t.occurrences(raceSchedule, new Date(2015, 2, 1), new Date(2015, 5, 31));

will produce:

[ Wed Mar 04 2015 00:00:00 GMT+0200 (SAST),
  Wed Mar 11 2015 00:00:00 GMT+0200 (SAST),
  Wed Mar 18 2015 00:00:00 GMT+0200 (SAST),
  Wed Mar 25 2015 00:00:00 GMT+0200 (SAST),
  Wed Apr 01 2015 00:00:00 GMT+0200 (SAST),
  Wed Apr 08 2015 00:00:00 GMT+0200 (SAST),
  Wed Apr 15 2015 00:00:00 GMT+0200 (SAST),
  Wed Apr 22 2015 00:00:00 GMT+0200 (SAST),
  Wed Apr 29 2015 00:00:00 GMT+0200 (SAST),
  Sat May 02 2015 00:00:00 GMT+0200 (SAST),
  Sat May 09 2015 00:00:00 GMT+0200 (SAST),
  Sat May 16 2015 00:00:00 GMT+0200 (SAST),
  Sat May 23 2015 00:00:00 GMT+0200 (SAST),
  Sat May 30 2015 00:00:00 GMT+0200 (SAST),
  Sat Jun 06 2015 00:00:00 GMT+0200 (SAST),
  Sat Jun 13 2015 00:00:00 GMT+0200 (SAST),
  Sat Jun 20 2015 00:00:00 GMT+0200 (SAST),
  Sat Jun 27 2015 00:00:00 GMT+0200 (SAST) ]

If we want to express that there won't be races during the Easter holidays:

var holidays = t.intersectionOf(
  t.onOrAfter(new Date(2015, 2, 30)),
  t.onOrBefore(new Date(2015, 3, 17))
)
var raceDays = t.intersectionOf(raceSchedule, t.negate(holidays))

Then

t.occurrences(raceDays, new Date(2015, 2, 1), new Date(2015, 5, 31))

will give us the occurrences:

[ Wed Mar 04 2015 00:00:00 GMT+0200 (SAST),
  Wed Mar 11 2015 00:00:00 GMT+0200 (SAST),
  Wed Mar 18 2015 00:00:00 GMT+0200 (SAST),
  Wed Mar 25 2015 00:00:00 GMT+0200 (SAST),
  Wed Apr 22 2015 00:00:00 GMT+0200 (SAST),
  Wed Apr 29 2015 00:00:00 GMT+0200 (SAST),
  Sat May 02 2015 00:00:00 GMT+0200 (SAST),
  Sat May 09 2015 00:00:00 GMT+0200 (SAST),
  Sat May 16 2015 00:00:00 GMT+0200 (SAST),
  Sat May 23 2015 00:00:00 GMT+0200 (SAST),
  Sat May 30 2015 00:00:00 GMT+0200 (SAST),
  Sat Jun 06 2015 00:00:00 GMT+0200 (SAST),
  Sat Jun 13 2015 00:00:00 GMT+0200 (SAST),
  Sat Jun 20 2015 00:00:00 GMT+0200 (SAST),
  Sat Jun 27 2015 00:00:00 GMT+0200 (SAST) ]

API Documentation

Is here.