curry.js

const curring = fn => {
    const { length } = fn
    const curried = (...args) => {
        return (args.length >= length
              ? fn(...args)
              : (...args2) => curried(...args.concat(args2)))
    }
    return curried
}

const listMerge = (a, b, c) => [a, b, c]
const curried = curring(listMerge)
console.log(curried(1)(2)(3)) // [1, 2, 3]

console.log(curried(1, 2)(3)) // [1, 2, 3]

console.log(curried(1, 2, 3)) // [1, 2, 3]