Functional programming "or" in Javascript

or.js

/*
An "or" function is a higher-order function that composes multiple predicates into one, 
such that the composed predicate will return true if at least one of the predicates 
returns true for the given argument. (A predicate is a function that returns `boolean`.)

e.g.
const isEven = n => n%2 === 0
const isPositive = n => n > 0

// un-fancy
items.filter(x => isEven(x) || isPositive(x))

// fancy
items.filter(or(isEven, isPositive))
*/

// simple
let or = (f, g) => x => f(x) || g(x)

// variable args
let or = (f, g) => (...args) => f(...args) || g(...args)

// variable predicates, variable args
or = (...fs) => (...args) => 
  fs.length > 0 && (
    fs[0](...args) || 
    or(fs.slice(1))(...args)
  )

/* 
Libraries:
- https://landau.github.io/predicate/#or
- https://github.com/Moeriki/node-fp-or
*/