Typescript API Design: Single Callable Or Multiple Callable

Let's start with an example, let's say the requirement is to create a ‘travel’ API where it takes ‘destination’ and ‘transportation’ as arguments.

Currying is the process of transforming a function into multiple callable, but here I refer to it as a function that returns another function based on the number of parameters.

How would you design the API, with Typescript, which pattern do you use?

A. plain simple function

const travel = (destination, transportation) => {
 // do something
}

B. curry form

const travel = (destination) => (transportation) => {
 // do something
}

C. method chaining

const travel = (destination) => {
 return {
 transport: (transportation)=>{
 // do something
      }
   }
}

currying and method chaining are similar, because it involves multiple callable, while plain function is only one callable.

I prefer single callable, for a very simple reason, less prone to error when you call it.

Here is how you call them, keep in mind we are using Typescript

A. plain function

travel(‘North Pole’, ‘swimming’) // ok
travel(‘North Pole’) // ts error

B. Currying

travel(‘North Pole’)(‘swimming’) // ok
travel(‘North Pole’)() // ts error
travel(‘North Pole’) // ok, but do nothing, no ts error

C. Method chaining

travel(‘North Pole’).transport(‘swimming’) // ok
travel(‘North Pole’).transport() // ts error
travel(‘North Pole’) // ok, but do nothing, no ts error

As you can see, it is impossible to call the plain function incorrectly with Typescript.

As you can see, it is impossible to call the plain function incorrectly with Typescript.

However this is not the same with currying and method chaining where it is possible to call them partially if you don’t pay attention

Still currying and method chaining are good for reusing arguments

const goToNorthPoleWith= travel(‘North Pole’)
goToNorthPoleWith(‘Airplane’)
goToNorthPoleWith(‘Ship’)

so to have the best of both worlds, we should always start from a single callable, and if we want to reuse the argument, we can curry it afterwards.