手写sumOf

实现函数计算：sum(2,5,6)(4).sumOf()

function sum (...arg) {
    const res = arg.reduce((a,b) => a+b,0)
    const fn = (...newArg) => {
        return sum(res, ...newArg)
    }
    fn.sumOf = () => res
    return fn
}
// 测试
console.log(sum(2,3)(4).sumOf())