선생님께서 let을 주로사용하라고해서 var대신 let을 넣었더니 실행이 안됩니다 왜그런거죠??

var name = "스파르타";

var job = "developer";

var user = {

 name,

 job

}

console.log(user);

//{name: "스파르타", job: "developer"}

VM5451:9 {name: '스파르타', job: 'developer'}

undefined

let name = "스파르타";

let job = "developer";

let user = {

 name,

 job

}

console.log(user);

//{name: "스파르타", job: "developer"}

VM5506:1 Uncaught SyntaxError: Identifier 'job' has already been declared