Variadic curried sum function

Question

I need a js sum function to work like this:

sum(1)(2) = 3
sum(1)(2)(3) = 6
sum(1)(2)(3)(4) = 10 
etc.

I heard it can\'t be done. But heard

Answer 1

function add(a) {
    let curry = (b) => {
        a += b
        return curry;
    }
    curry[Symbol.toPrimitive] = (hint) => {
        return a;
    }
    return curry
}

console.log(+add(1)(2)(3)(4)(5));        // 15
console.log(+add(6)(6)(6));              // 18
console.log(+add(7)(0));                 // 7
console.log(+add(0));                    // 0