@kyleshevlin/kase

A simple, type-safe pattern-ish matching function.

const result = kase(person.age)
  .when(1, () => "You're just a baby!")
  .when(
    x => x < 18,
    () => "You've gotten so big!"
  )
  .when(
    x => x < 65,
    () => "So how's work?"
  )
  .when(
    x => x < 90,
    age => `Holy smokes, You don't look a day over ${age - 10}!`
  )
  .otherwise(() => 'Uhh, do you even have a pulse?')

API

Note: It might be to your benefit to take a look at the types in kase.ts.

kase

function kase(input) {}

kase takes an input which is any value, and stores it to be compared to the patterns passed to the when and otherwise methods.

when

function when(pattern, callback) {}

when receives a pattern to compare to the input. A pattern can either be a value of the same type as input, or a predicate function that receives the input as an argument. If the pattern argument is a value, it is matched strictly against the input with ===.

when also receives a callback function which should return the desired result should a match be found. The first when to match is the result of the kase chain.

otherwise

function otherwise(callback) {}

otherwise is how we provide a default result. It receives a callback exactly like when. otherwise will return the result of the callback as the result of the entire chain.

end

function end() {}

If no otherwise is provided, end is necessary to complete the chain and return the result. Like so:

const result = kase(Math.random())
  .when(
    x => x <= 0.33,
    () => 'low'
  )
  .when(
    x => x <= 0.67,
    () => 'mid'
  )
  .when(
    x => x <= 0.99,
    () => 'high'
  )
  .end() // would return `undefined` in the cases where x is > .99