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?')

npm install @kyleshevlin/kase

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

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.

function when(pattern, resolution) {}

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 resolution. This can be a value or a function that receives the argument passed to kase and returns the desired result. The first when to match is the result of the kase chain.

function otherwise(resolution) {}

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

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