从firebase获取价值

Question

我想要获取Firebase中某个函数以外的值，以便在全局范围内使用，但它不起作用。

var ref = new Firebase("https://xxxxx.firebaseio.com/users/xxxx/roles/admin/"); // true or false 

    ref.once("value", function(snapshot) { 
    console.log("here"); 
    console.log(snapshot.val()); 
    var isAdmin = snapshot.val(); 
    return isAdmin; 
}); 

console.log(isAdmin); /// cannot get value 

Answer 1

不能使用isAdmin之外，因为它是不可用，用它在回调

ref.once("value", function(snapshot) { 
    //You should wrap you code here, to use isAdmin variable 
    //You can do whatever with isAdmin, but you can't return it. 
    //It's callback that running asynchronously 
    console.log(isAdmin) 
})