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())