JavaScript one-line curry (ES6)

curry.js

const curry = (fn, arity = fn.length) => (...args) => args.length >= arity ? fn(...args) : (...moreArgs) => curry(fn)(...args, ...moreArgs)

// tests
const _add = (a, b, c) => a + b + c

describe('curry', () => {
  it('should currify the input function', () => {
    const add = curry(_add)
    expect(add(1, 2, 3)).toBe(6)
    expect(add(1)(2)(3)).toBe(6)
    expect(add(1, 2)(3)).toBe(6)
    expect(add(1)(2, 3)).toBe(6)
  })
})