我正在为我的应用程序使用Firebase身份验证。 似乎有一个无限循环，页面不断被重定向

Question

The following function is to redirect the user to "Select Stream.html" when the user logs in.It keeps on replacing the location over and over again.

firebase.auth().onAuthStateChanged(function(user) {
    if (user) {
        window.location.replace("Select Stream.html");
      // User is signed in.
    } else {
      // No user is signed in.
      window.location.replace("index.html");
    }
  });

I am new to coding.

 Here is the Log in Function function login() { var userEmail=document.getElementById("email-field").value; var userPassword=document.getElementById("password-field").value; firebase.auth().signInWithEmailAndPassword(userEmail, userPassword).catch(function(error) { // Handle Errors here. var errorCode = error.code; var errorMessage = error.message; /* window.location='Select Stream.html'; */ window.alert("Error : " + errorMessage); // ... }); } The Login function will be triggered when the signin-button is clicked. 

 <input onclick="login()" type="submit" name="signin-button" value="Sign In"/> 

Answer 1

First, change the name of Select Stream.html to have no spaces or capital letters. This is common practice, and I recommend changing the name of the file to select_stream.html .

Before opening select_stream.html or index.html , check whether the user is already on that page to prevent the page from refreshing, like this:

if (user) {
  // User is signed in.
  if(window.location.href.indexOf("select_stream.html") == -1){
    window.location.replace("select_stream.html");
  }
} else {
  // No user is signed in.
  if(window.location.href.indexOf("index.html") == -1){
    window.location.replace("index.html");
  }
}

The window.location.href variable refers to the URL of the current page, and the .indexOf function allows you to check if a value is contained inside the URL. The .indexOf function returns -1 if the specified value could not be found within the string, so this code simply only redirects if the user is not already on the redirect page.