Time Walk

What is this?

Time Walk is a simple library for generating date recurrance rules. I was inspired to write this after having previously used Rrule for a work project and found Rrule to have it's quirks. This module heavily leverages the moment-timezone library and aims to keep this library as lightweight as possible.

See Rrule library here

See differences to Rrule here

What would I use this for?

There are a number of potential use cases for this module, two better examples I can think of are...

• Generating calendar appointments based on a defined pattern (rule).
• Implementing a scheduled jobs service in your app, where timezone support is important. Cron doesn't support fortnightly intervals or multi-timezone.

Try it out

See runkit demo here

How do I use it?

Syntax

Install

yarn add time-walk OR npm install --save time-walk

Creating a Rule

Arguments for a new rule are...

• start a moment-timezone object where the date and timezone align to the first occurance you want the rule to generate. The timezone specified in the moment-timezone object will be used to generate all occurrences (dates) by Time Walk. See moment-timezone for more details.
• an interval, starting from the start date, how far apart do we want occurrence (date) to be (must be in a format moment.js understands, see moment docs here.

For example, if I want a rule that recurs on the 1st of every month according to the time in Sydney, Australia, and I wan't my rule to start from next month (July 2017), I would input...

const moment = require('moment-timezone');
const { TimeWalk } = require('time-walk');
 
const start = new moment.tz('2017-07-01', 'Australia/Sydney');
const rule = new TimeWalk(start, { months: 1 });

OR if I want a rule that recurs every second Monday (fortnightly), starting in July 2017 in UTC.

const moment = require('moment-timezone');
const { TimeWalk } = require('TimeWalk');
 
const start = new moment.tz('2017-07-03', 'UTC');
const rule = new TimeWalk(start, { weeks: 2 });

Note: the 3rd of July is the first Monday in July, so this needs to be the start date.

Getting (n)th Occurance

If I want to get the 2nd occurance of my rule...

const start = new moment.tz('2017-07-01', 'Australia/Sydney');
const rule = new TimeWalk(start, { months: 1 });
 
const result = rule.occurance(2) // result === 2017-08-01 in Australia/Sydney Time

Note: The start date counts as the first occurence.

Getting the first (x) Occurances

If I want to get the first three ooccurances of my rule...

const start = new moment.tz('2017-07-01', 'Australia/Sydney');
const rule = new TimeWalk(start, { months: 1 });
 
const result = rule.first(3)
// result === [2017-07-01, 2017-08-01, 2017-09-01] in Australia/Sydney Time

Note: The start date counts as the first occurence.

Getting Occurances within a Range

If I want to get ALL occurences for my rule that exist between two dates. For example, to get all occurences in July I would do...

const start = new moment.tz('2017-07-01', 'Australia/Sydney');
const rule = new TimeWalk(start, { weeks: 1 });
 
const from = new moment.tz('2017-07-01', 'Australia/Sydney');
const to = new moment.tz('2017-08-01', 'Australia/Sydney');
const result = rule.between(from, to);
 
// result === [2017-07-01, 2017-07-08, 2017-07-15, 2017-07-22, 2017-07-29]
// in Australia/Sydney Time

Converting to a string

This is useful if you want to store rules in a database. You may also need to store the last occurance generated via the rule, but that must be handled separately.

const start = new moment.tz('2017-07-01', 'Australia/Sydney');
const rule = new TimeWalk(start, { months: 1 });
 
const result = rule.toString();
// result === "START=2017-06-30T14:00:00.000Z;INTERVAL=M1;TZ=Australia/Sydney;"

Parse a rule (convert from a string)

const { parse } = require('time-walk');
 
const rule = parse("START=2017-06-30T14:00:00.000Z;INTERVAL=M1;TZ=Australia/Sydney;");
// rule === new TimeWalk(new moment.tz('2017-07-01', 'Australia/Sydney'), { months: 1 });

Why am I doing this?

At present I'm doing this purely as a personal challenge at this point, it's an interesting problem to solve but as I'm not doing this for work, and thus not spending work time on it, set expectations accordingly.

How can I help?

Send me a pull request! Please don't send me a pull request without tests though.

What's changed?

View Changelog

What still needs doing...

• Allow setting a default output type in constructor

• Add setter method (including setting default output type)

• Test between from and to validations

• Test interval is required (in constructor)

• Limit how many occurances get returned to 100?

• Document specifying output format

• Add .fromString to create a rule with a date in string format + timezone.

• remove use of decimals in calcs so more accurate?

• compile to ES2015

• Use CircleCI