编辑代码

// sum(x,y)和sum(x)(y)
function sum(){
    let arg = arguments
    if(arg.length===2) return arg[0] + arg[1]
    else{
        return function (a) {
         return arg[0] + a
        }
    }
}
console.log(sum(1,2))
console.log(sum(1)(2))