关于javascript:编写一个方法sum使sum123-和-sum123的输出都为6

function sum(){var _args = Array.prototype.slice.call(arguments)
    console.log(_args)

    var add =  function(){_args.push(...arguments)

        return add
    }
    add.valueof = function(){return _args.reduce((a,b)=>{return a+b})

    }
    return add
}
console.log(sum(1,2)(3).valueof())