Headless Calendar

A simple and easy to use JavaScript library that provides common calendar functionalities for making completely customizable calendar UI. Based heavily on the work done by https://github.com/ashutoshbw/headless-calendar

💡 Features

* It does all the calculations for finding the position of a day in a calendar.
* A calendar is an iterable. So you can use for of loop or the spread syntax to easily iterate over the days.
* You can choose which day to start a week with.
* Provides handy calendar classes for generating calendar of any month, year, last year or any period of time supported by original JavaScript Date object.
* It is based on original JavaScript Date but provides an abstraction over by excluding all the parts that doesn't needed or are not intuitive.

Installation

``
N/A for now
`

Meet the tools

Classes | Description
--- | ---
Calendar | It is the generic class for generating any arbitrary calendar from any date to any future date.
CalendarOfMonth | It generates calendar of any given month.
CalendarOfYear | It generates calendar of any given year.
PlainDate | It is a simple wrapper around the JavaScript Date. You can use it to find the difference between two dates, next, previous days and some other helpful things.

You can fetch the above classes using both ES6 and CommonJS module syntax.

🦉 Concepts

To understand how to use headless-calendar effectively, it will be helpful to picture a calendar as a two dimensional diagram like below:
`
+-------------------------> Day Axis
| 0 1 2 3 4 5 6 ---> Day Axis indices. Starts with 0.
| V V V V V V V
| Su Mo Tu We Th Fr Sa ---> Day Names
| 1 2 3 4 ---> 0
| 5 6 7 8 9 10 11 ---> 1
| 12 13 14 15 16 17 18 ---> 2
| 19 20 21 22 23 24 25 ---> 3
| 26 27 28 29 30 31 ---> 4
| |
V V
Week Axis Week Axis indices. Starts with 0 too.
`

Examples

`javascript
import {CalendarOfMonth} from "@onsetsoftware/headless-calendar";

// generates the calendar of January of 2021
const month = new CalendarOfMonth(2021, 1);

for (day of month) {
console.log(day);
}

/*
Day {
date: PlainDate { year: 2021, month: 1, date: 1 },
dayNumber: 1, // it counts the day
dayOfTheWeek: 1, // the day of the week from 0-6 = Sun - Sat
dayAxisIndex: 5, // the day axis index as explained in the above diagram
weekAxisIndex: 0 // the week axis index as explained in the above diagram
}
.
.
.
*/
`

The day object holds the necessary information about it's position on the calendar. This pattern of accessing days are same for all the calendar classes.

And as any calendar is an iterable you can also use it like below:
`javascript
// console logs only dates that are Sundays
[...month].forEach(day => {
if (day.dayAxisIndex == 0) {
console.log(day.date.date);
}
})
`

Calendar

This class is used to generate a calendar starting with any date to any future date. All the other calendar classes are derived from it.

Syntax:
`
new Calendar(startDateString, endDateString, [startWeekDayIndex])
`


$3


* startDateString(String) and endDateString(String): They should follow the format year-month-date format. Each part is expressed with digits. endDateString must represent a equal or later date than startDateString.
startWeekDayIndex(Number) Optional*: It represents the day to start the week with. 0 means Sunday and it goes on incrementally until 6 means Saturday.

$3

An iterable object. It has the following properties:
* startDate: It is the PlainDate version of starting date.
* endDate: It is the PlainDate version of ending date.
* startWeekDayIndex: It keeps record of the startWeekDayIndex parameters value. It that is not provided it defaults to zero.
maxWeekAxisIndex: This returns last week's week axis index*.
* weekDayNames: It returns an array of day names with the starting day as you specified with the startWeekDayIndex parameter.
* length: It returns the number total days in the calendar.

And it has a toString() method for easily seeing the output of a calendar. For example:

`javascript
import {Calendar} from "@onsetsoftware/headless-calendar";

const cal = new Calendar("2021-1-1", "2021-2-10");
console.log(cal.toString());
/*
Su Mo Tu We Th Fr Sa
1 2 January 2021
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
31 1 2 3 4 5 6 February
7 8 9 10
*/
`

The iterable is used to iterate over the days of the calendar. Each item of the sequence of this iterable is an object that represents a day. These day objects comes with the following properties and methods:

#### Properties
* date: A PlainDate representing that day.
dayNumber: If it is n, it means it's the n*th day of the calendar.
* dayOfTheWeek: the number 0-6 indicating Sunday (0) - Saturday (6).
dayAxisIndex: It is the day axis index* of the day as shown in diagram.
weekAxisIndex: It is the week axis index* of the day as shown in diagram.

#### Methods
* isFirstDayOfWeekAndMonth(): It returns a Boolean value indicating if the day is the 1st day of the week and also the 1st day of the month. This value is useful if you want to show month names right above such days.

CalendarOfMonth

This class is used to generate a calendar of the specified month.

Syntax:
`
new CalendarOfMonth(year, month, [startWeekDayIndex])
`

$3


* year(Number) and month(Number): The year and month number for generating the calendar. Note that unlike in JavaScript, here month starts with 1(January).
startWeekDayIndex(Number) Optional*: It represents the day to start the week with. 0 means Sunday and it goes on incrementally until 6 means Saturday.

$3

An iterable object with the same interface of a Calendar instance representing the days of the specified month.

It's toString() method formats the calendar a little differently than the original Calendar class:
`javascript
import {CalendarOfMonth} from "@onsetsoftware/headless-calendar";

const month = new CalendarOfMonth(2021, 1);
console.log(month.toString())

/*
January 2021
Su Mo Tu We Th Fr Sa
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
31
*/
`

CalendarOfYear

This class is used to generate a calendar of the given year.

Syntax:
`
new CalendarOfYear(year, [startWeekDayIndex])
`

$3


* year(Number): The year number for generating the calendar.
startWeekDayIndex(Number) Optional*: It represents the day to start the week with. 0 means Sunday and it goes on incrementally until 6 means Saturday.

$3

An iterable object with the same interface of a Calendar instance, representing the days of the specified year.

PlainDate


PlainDate is wrapper class around the original JavaScript Date. It only thinks about year, month and date. No hours, minutes or others parts.

Syntax:
`
new PlainDate(dateString: DateString, locale?: Intl.LocalesArgument)
`


$3


dateString(String) Optional*: It should follow the format year-month-date format. Each part is expressed with digits. If it is omitted, it is treated as current date according to local time.

$3

An instance of PlainDate. It it only has three properties year, month and date holding the corresponding given information.

A PlainDate instance has the following methods:
#### toJSDate
It converts a PlainDate to JavaScript date.

Syntax:
`javascript
somePlainDate.toJSDate()
`
##### Parameters
No parameter
##### Return value
JavaScript version of the PlainDate.

#### equals
Checks whether two PlainDates are equal or not.

Syntax:
`javascript
somePlainDate.equals(another)
`
##### Parameters
* another(PlainDate): Another PlainDate value to compare to.
##### Return value
A Boolean value indicating whether the PlainDate equals another PlainDate.

#### isBefore
Checks whether the given PlainDate is before the current one.

Syntax:
`javascript
somePlainDate.isBefore(another)
`
##### Parameters
* another(PlainDate): Another PlainDate value to compare to.
##### Return value
A Boolean value indicating whether the PlainDate is before another PlainDate.

#### isAfter
Checks whether the given PlainDate is after the current one.

Syntax:
`javascript
somePlainDate.isBefore(another)
`
##### Parameters
* another(PlainDate): Another PlainDate value to compare to.
##### Return value
A Boolean value indicating whether the PlainDate is after another PlainDate.

#### diff
Returns the difference between two PlainDates.

Syntax:
`
somePlainDate.diff(another);
`

##### Parameters
* another(PlainDate): Another PlainDate value to find the difference.
##### Return value
The difference between the two PlainDates. Note that the boundary dates are included in the counting.

#### next
Returns the next PlainDate.

Syntax:
`
somePlainDate.next();
`

##### Parameters
None.

##### Return value
The next PlainDate.

#### previous
Returns the previous PlainDate.

Syntax:
`
somePlainDate.previous();
`

##### Parameters
None.

##### Return value
The previous PlainDate.

#### addDays
Returns the day days after the active PlainDate.

Syntax:
`
somePlainDate.addDays(days);
`

##### Parameters
* days(number): The number of days to add

##### Return value
The PlainDate days after the active date.

#### subDays
Returns the day days before the active PlainDate.

Syntax:
`
somePlainDate.subDays(days);
`

##### Parameters
* days(number): The number of days to subtract

##### Return value
The PlainDate days before the active date.

#### toString
A string representation of the PlainDate as a DateString.

Syntax:
`
somePlainDate.toString();
`

##### Parameters
None.

##### Return value
A string representation of somePlainDate with the year-month-date format where each part is made of digits. year is full year.

$3


#### fromJSDate
Returns a plain date from a JavaScript date.

Syntax:
`javascript
PlainDate.fromJSDate(date, [UTC])
`

##### Parameters
* date(Date): A JavaScript Date instance.
UTC(Boolean) Optional*: By default it is true, that means the date is treated as UTC time. If you want local time, set it to false.

##### Return value
The PlainDate version of the JavaScript date according to UTC or local time(based on the 2nd parameter).

#### today
Returns today in PlainDate.

Syntax:
`javascript
PlainDate.today([UTC])
`

##### Parameters
UTC(Boolean) Optional*: By default it is true, that means we will get result in UTC time. If you want local time set it to false.

##### Return value
Today in PlainDate` according local time or UTC time(based on the 1st parameter).

License

MIT