Node.js中Json通过字符串赋值的问题

有一个JSON格式的变量userinfo

var userinfo = {
    "USERNAME"  : "",
    "EMAIL"  : "",
    "SALT"  : "",
    "HASH"  : "",
    "DEVICEID"  : "",
    "TOKIN"  : ""
};

然后还有一个字符串变量data的内容{"USERNAME":"abc","EMAIL":"xxx@gmail.com","SALT":"b9L7RqfCAIeJ72R1q8pqru3ZyZJJ6VCpyV/YBdIjMDbnGx5UwtnO7+883Q0e2kSoji25/L4NK4ZSebrBYjBifdd7Jn9VJDDLYu0sA76LgmMGswp6zzAEosFa3AHMUh0lNStf+8K3OhvPA1ER3IfjJN0Y33u14cYdLxGshCinT4I=","HASH":"+b5cNtArzhKJAZEegaIE/DtTRC+dRP0bjydOhGiyJptMYoTw9pPyjIKpZWMGNp9PK7MI1TKidq03wCr3jFeAisP2nMXRmsZFmhTLhzgtrGsxFomz0cZiEtqqSNiBkXiPtr/V7mwgiXqFbxf3om17CP9diR+1enjY2Br6zBoaq8A=","DEVICEID":"","TOKIN":"25230B4D629F59876948C2A3BA2A33E8"}

我想把data的内容放到userinfo的对应位置上，该怎么做？
data里面的内容是之前把这个userinfo保存成的字符串。

或者换句话说我现在想用USERNAME字段的内容，改怎么用呢？

---

for(x in userinfo){
       if(data[x]){
        userinfo[x] = data[x];
    }
}
console.log(userinfo['USERNAME']);

是这样的么？

---

var jsonn = '{"USERNAME":"abc","EMAIL":"xxx@gmail.com","SALT":"b9L7RqfCAIeJ72R1q8pqru3ZyZJJ6VCpyV/YBdIjMDbnGx5UwtnO7+883Q0e2kSoji25/L4NK4ZSebrBYjBifdd7Jn9VJDDLYu0sA76LgmMGswp6zzAEosFa3AHMUh0lNStf+8K3OhvPA1ER3IfjJN0Y33u14cYdLxGshCinT4I=","HASH":"+b5cNtArzhKJAZEegaIE/DtTRC+dRP0bjydOhGiyJptMYoTw9pPyjIKpZWMGNp9PK7MI1TKidq03wCr3jFeAisP2nMXRmsZFmhTLhzgtrGsxFomz0cZiEtqqSNiBkXiPtr/V7mwgiXqFbxf3om17CP9diR+1enjY2Br6zBoaq8A=","DEVICEID":"","TOKIN":"25230B4D629F59876948C2A3BA2A33E8"}';
var userinfo = JSON.parse(jsonn);