javascript - 如何在其功能之外使用父 key 请求的结果

Question

以下内容获取子节点的父键。有没有办法将结果(父键)放在函数之外，例如全局变量或其他东西。我希望能够调用一个返回父键的函数

这有效(在控制台中返回parent.key)

firebase.auth().onAuthStateChanged(function(user){
    var ref = firebase.database().ref('users');
    ref.orderByChild('uid').equalTo(user.uid).on("value", function(snapshot) {
        snapshot.forEach((function(child) { console.log(child.key) }));
    });
});

这不起作用

var test;
firebase.auth().onAuthStateChanged(function(user){
    var ref = firebase.database().ref('users');
    ref.orderByChild('uid').equalTo(user.uid).on("value", function(snapshot) {
        snapshot.forEach((function(child) { test = child.key }));
    });
});
console.log(test);

Answer 1

以下应该有效

function f_returnUserDetails(a){
    var key;
    var childData;
    return new Promise(function(resolve, reject) { 
        firebase.database().ref('/users/').orderByChild("uid").equalTo(a).on('value', function (snapshot) {
            snapshot.forEach(function(childSnapshot) {
                key = childSnapshot.key;
                childData = childSnapshot.val();
                resolve([childData, childSnapshot.key]);
            });
        });
    });
};


firebase.auth().onAuthStateChanged(function(user){
    var user = firebase.auth().currentUser;
    var uid = user.uid;
    f_returnUserDetails(uid).then((dbItems) => {
        console.log(dbItems[1])
    });
});