firebase.initializeApp回调/承诺？

本文介绍了firebase.initializeApp回调/承诺？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

这是我的网页

 <！DOCTYPE html> 
< html> 
< head> 
< meta charset =utf-8> 
< meta http-equiv =X-UA-Compatiblecontent =IE = edge> 
< meta name =viewportcontent =width = device-width，initial-scale = 1> 
< title> Calcolo Diliuzioni< / title> 
 
< / head> 
< body> 
 
< h1>我的应用< / h1> 
 
 < script src =https://apis.google.com/js/platform.jsasync defer>< / script> 
 
 < script src =https://www.gstatic.com/firebasejs/live/3.0/firebase.js>< / script> 
< script> 
 //初始化Firebase 
 var config = {
 apiKey：，
 authDomain：，
 databaseURL：，
 storageBucket： ，
}; 
 firebase.initializeApp（config）; 
< / script> 
 
< script type =text / javascript> 
 var user = firebase.auth（）。currentUser; 
 if（user）{
 console.log（user）; 
} else {
 console.log（user）; 
} 
< / script> 
< / body> 
< / html>

假设我有一个已经登录的用户。当我在控制台中加载页面时，我得到了 null 。如果我在浏览器控制台中运行相同的代码

pre> var user = firebase.auth（）。currentUser; if（user）{ console.log（user）; } else { console.log（user）; }

我可以获取当前用户的对象。
$ b我认为 firebase.initializeApp（config）; 有一些异步行为。什么是正确的解决方法？我应该在 firebase.initializeApp（config）; 函数上使用承诺或其他东西吗？一种回调。

解决方案

initialize app是同步的。但是，确定当前用户状态是异步的。确定当前auth状态的正确方法是使用观察者：

  firebase.auth （）.onAuthStateChanged（function（user）{
 if（user）{
 //用户登录且currentUser不再返回null 
} else {
 //没有用户登录。
} 
}）;

This is my web page

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <title>Calcolo Diliuzioni</title>

    </head>
    <body>

        <h1>My app</h1>

        <!-- Libreria per gestire l'autenticazione con google -->
        <script src="https://apis.google.com/js/platform.js" async defer></script>

        <!-- Firebae config -->
        <script src="https://www.gstatic.com/firebasejs/live/3.0/firebase.js"></script>
        <script>
        // Initialize Firebase
        var config = {
        apiKey: "",
        authDomain: "",
        databaseURL: "",
        storageBucket: "",
        };
        firebase.initializeApp(config);
        </script>

        <script type="text/javascript">
            var user = firebase.auth().currentUser;
            if (user) {
                console.log(user);
            } else {
                console.log(user);
            }
        </script>
    </body>
</html>

Let's assume I have an already logged user. When I load the page in the console I got null. While I'm expecting to have the current user's object.

If I run the same code in the browser console

var user = firebase.auth().currentUser;
if (user) {
    console.log(user);
} else {
    console.log(user);
}

I'm able to get the current user's object.

I think that the firebase.initializeApp(config); has some async behavior. What's the right way to work around it? Should I use a promise or something on the firebase.initializeApp(config); function? A sort of callback..

解决方案

initialize app is synchronous. However, determining the current user state is asynchronous. The right way to determine the current auth state is to use an observer:https://firebase.google.com/docs/auth/web/manage-users

firebase.auth().onAuthStateChanged(function(user) {
  if (user) {
    // User is signed in and currentUser will no longer return null.
  } else {
    // No user is signed in.
  }
});

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