Arity matching functions in JavaScript

arityMatch.js

// Example 1 or 2-arity function f
const f = (...args) =>
  [
    (x)     => console.log("One param"),
    (x, y)  => console.log("Two params")
  ][args.length-1](...args);

f(1)    // "One param"
f(1, 2) // "Two param"


// Abstracted into a higher order function
const arityMatch = (...fns) =>
  (...args) =>
    [...fns][args.length-1](...args);

const f2 = arityMatch(
  (x)     => console.log("One param"),
  (x, y)  => console.log("Two param")
);

f2(1)    // "One param"
f2(1, 2) // "Two param"