// First we need to know the number of arguments of the function.
// Thankfully, functions have a length parameter that tells us just that.
const curry = (fn, length = fn.length) => (...args) => {
    if (args.length >= length) {
        return fn(...args);
    }

    return curry((...nextArgs) => fn(...args, ...nextArgs), fn.length - args.length);
}

const add = curry((a, b, c) => a + b + c);
add(1)(2)(3); // 6
add(1, 2, 3); // 6
add(1, 2)(3); // 6
add(1)(2, 3); // 6