Alternatives to `setDefaultOptions` for Flexible Date Handling in date-fns

Purpose

• These arguments are:
  • locale: This determines how dates are formatted based on language and region.
  • weekStartsOn: This specifies the first day of the week (0 for Sunday, 1 for Monday, etc.).
  • firstWeekContainsDate: This defines which day of January should always be included in the first week of the year.
• This function sets default options for three commonly used arguments across various date-fns functions.

Benefits

• By setting defaults, you can ensure consistent behavior for these options throughout your application without having to pass them explicitly to every date-fns function you use.

How it works

1. Import: You can import setDefaultOptions from the date-fns/setDefaultOptions module.
2. Arguments: It takes a single argument, which is an object containing the desired default options.
   • locale: This should be a valid locale object as defined by date-fns (you can import specific locales from date-fns/locale).
   • weekStartsOn: An integer between 0 and 6, representing the day (Sunday = 0, Monday = 1, etc.).
   • firstWeekContainsDate: An integer between 1 and 31, specifying the day of January in the first week.

Example

import { es } from 'date-fns/locale' // Import Spanish locale
setDefaultOptions({
  locale: es,
  weekStartsOn: 1, // Start the week on Monday
  firstWeekContainsDate: 4, // Include January 4th in the first week
})

const formattedDate = format(new Date(2024, 5, 30), 'P') // Monday, Jun 30, 2024 (formatted in Spanish)

• setDefaultOptions is considered a non-pure function because it modifies global settings. This means subsequent calls to date-fns functions will use the newly set defaults.

---

Overriding Defaults

This code shows how manually passed options can override the default options:

setDefaultOptions({ weekStartsOn: 1 }) // Set Monday as default week start

const result1 = startOfWeek(new Date(2024, 5, 30)) // Monday, Jun 24, 2024 (using default)

const result2 = startOfWeek(new Date(2024, 5, 30), { weekStartsOn: 0 }) // Sunday, Jun 23, 2024 (overrides default)

Removing Defaults

setDefaultOptions({ weekStartsOn: 1 }) // Set Monday as default
setDefaultOptions({ weekStartsOn: undefined }) // Remove weekStartsOn default

const result = startOfWeek(new Date(2024, 5, 30)) // Uses system default for week start

Using getDefaultOptions

This code demonstrates retrieving the currently set default options:

import { setDefaultOptions, getDefaultOptions } from 'date-fns/setDefaultOptions'

setDefaultOptions({ locale: enGB }) // Set English (Great Britain) locale

const currentOptions = getDefaultOptions()
console.log(currentOptions.locale) // Output: en-GB

---

Passing Options Explicitly

• This is the most straightforward approach. Pass the desired options (locale, weekStartsOn, firstWeekContainsDate) directly as arguments to each date-fns function you use.

import { format, startOfWeek } from 'date-fns'
import { enGB } from 'date-fns/locale' // Import English (Great Britain) locale

const formattedDate = format(new Date(2024, 5, 30), 'P', { locale: enGB }) // Monday, Jun 30, 2024 (formatted in English)

const weekStart = startOfWeek(new Date(2024, 5, 30), { weekStartsOn: 1 }) // Monday, Jun 24, 2024 (week starts on Monday)

Creating Custom Wrapper Functions

• If you frequently use specific options with certain date-fns functions, create custom wrapper functions. These functions can encapsulate the repetitive code and improve readability.

import { format, startOfWeek } from 'date-fns'
import { enGB } from 'date-fns/locale' // Import English (Great Britain) locale

const formatDateWithLocale = (date) => format(date, 'P', { locale: enGB })

const getStartOfWeekMonday = (date) => startOfWeek(date, { weekStartsOn: 1 })

const formattedDate = formatDateWithLocale(new Date(2024, 5, 30)) // Monday, Jun 30, 2024 (formatted in English)

const weekStart = getStartOfWeekMonday(new Date(2024, 5, 30)) // Monday, Jun 24, 2024 (week starts on Monday)

Managing Options with State Management

• In larger applications, consider using a state management solution like Redux or MobX to store and manage these options globally. This allows centralized control and easier updates.

• Consider state management for complex scenarios with dynamic options.
• Use explicit options or wrappers for frequent, specific configurations.
• Use setDefaultOptions for consistent defaults across a smaller project.