小编Rah*_*rma的帖子

firebase.auth().onAuthStateChanged(function(user) {
  if (user) {
    // User is signed in.
      console.log("Hurray ! signed in successfully !");
  } else {
    // No user is signed in.
     console.log("Sign in required !");
     $("#login-btn-nav").click();
  }
});



$("#login-btn").on('click',function(){
    console.log("Hello");
    var email = $("#email-input").val();
    var password = $("#password-input").val();

    if(email != "" && password != ""){
    		firebase.auth().signInWithEmailAndPassword(email, password).catch(function(error) {
				  // Handle Errors here.
				  var errorCode = error.code;
				  var errorMessage = error.message;
				  // ...
				  window.alert("Following error encountered : "+errorMessage+" .");
				});
    		}
});

<script src="https://www.gstatic.com/firebasejs/4.2.0/firebase.js"></script>
<script src="https://www.gstatic.com/firebasejs/4.2.0/firebase-app.js"></script>
<script …

var flag = false;
(function(){
    console.log(flag);
    var flag = true; // JavaScript only hoists declarations, not initialisations

    console.log(flag);

    if(flag){
        let name = "John";
        const age = "24";

        console.log(name);
        console.log(age);
    }

    //console.log(name); //ReferenceError: name is not defined ( as name is block scoped here )
    //console.log(age);  //ReferenceError: age is not defined ( as age is block scoped )

})();