离子3 + firebase不能分配属性＆＃34; key＆＃34; 0：不是对象

Question

这是我的结构

{ "employes" : {
  "-LDpxa5AEJNq2A8x4Xk7" : {
    "service" : "COMPTA",
    "users" : {
      "-LDq26auYY1cSeVTK8QU" : {
        "age" : 40,
        "name" : "Dupont"
      },
      "-LDq2F64dOiMeAKjiWS6" : {
        "age" : 35,
        "nom" : "Durand"
      }
    },
    "city" : "Montpellier",
    "country" : "France"
  },
  "-LDq8DJ7_Z4cqnd1AYI6" : {
    "service" : "INFO",
    "users" : {
      "-LDq26auYY1cSeVTK8QU" : {
        "age" : 35,
        "name" : "Martin"
      },
      "-LDq2F64dOiMeAKjiWS6" : {
        "age" : 38,
        "nom" : "Dunaud"
      }
    },
    "city" : "Reims",
    "country" : "France"
  }
}

}

这是我的代码的一部分

constructor(public navCtrl: NavController, public navParams: NavParams) {
firebase.database().ref('employes/'+this.navParams.get("servicekey")+'/users/'+this.navParams.get("userkey")+'/').on(
'value', resp => {
this.users = [];
this.users = snapshotToArray(resp);
});}    



export const snapshotToArray = snapshot => {
let returnArr = [];
    snapshot.forEach(childSnapshot => {
      let item = childSnapshot.val();
      item.key = childSnapshot.key;
    returnArr.push(item);
});

return returnArr;};

我尝试获取用户的姓名和年龄。 我的参考值没问题 聘用过的员工/ -LDpxa5AEJNq2A8x4Xk7 /用户/ -LDq2F64dOiMeAKjiWS6

我用＆＃34; let item = childSnapshot.val（）;＆＃34;得到我的节点的值。 但是＆＃34; item.key = childSnapshot.key;＆＃34;给我错误

无法分配属性＆＃34; key＆＃34;在0：不是对象

有人帮我吗？