@algosail/date

Date comparison and parsing utilities. All comparisons are based on milliseconds since epoch (valueOf()).

Contents

• equals
• lte / lt / gte / gt
• min / max / clamp
• parseDate

equals

equals :: Date -> Date -> Boolean

True when both dates represent the same instant.

equals(new Date(0))(new Date(0)) // => true
equals(new Date(0))(new Date(1)) // => false

const d = new Date('2024-01-01')
equals(d)(new Date('2024-01-01')) // => true
equals(d)(new Date('2024-01-02')) // => false

lte / lt / gte / gt

lte :: Date -> Date -> Boolean
lt  :: Date -> Date -> Boolean
gte :: Date -> Date -> Boolean
gt  :: Date -> Date -> Boolean

Temporal comparisons.

const d1 = new Date('2024-01-01')
const d2 = new Date('2024-06-01')

lte(d1)(d2) // => true   (d1 is before or equal to d2)
lte(d2)(d1) // => false
lt(d1)(d2) // => true
lt(d1)(d1) // => false  (not strictly before itself)

gte(d2)(d1) // => true
gt(d2)(d1) // => true
gt(d1)(d1) // => false

min / max / clamp

min   :: Date -> Date -> Date
max   :: Date -> Date -> Date
clamp :: Date -> Date -> Date -> Date

const jan = new Date('2024-01-01')
const jun = new Date('2024-06-01')
const dec = new Date('2024-12-01')

min(jan)(jun) // => jan
max(jan)(jun) // => jun

clamp(jan)(jun)(dec) // => jun  (dec is after hi)
clamp(jan)(jun)(jan) // => jan  (on lo boundary)
clamp(jan)(dec)(new Date('2024-03-15')) // => new Date('2024-03-15')  (in range)

parseDate

parseDate :: String -> Maybe Date

Parses a date string — Just(Date) on success, Nothing for invalid input.

parseDate('2020-01-01') // => just(new Date('2020-01-01'))
parseDate('2024-12-31T23:59:59') // => just(Date)
parseDate('not a date') // => nothing()
parseDate('') // => nothing()