How to to logged in users that has verified email only

I have a function that enable user to sign up or create an account. It also sends verification after signing up. I only want users whose email were verified to logged in.What would I do?

This is my login function.

   function signIn() {
   var email = $("#emailtxt").val();
   var password = $("#passwordtxt").val();
   var auth = firebase.auth();        

   firebase.auth().signInWithEmailAndPassword(email, 
   password).then(function(value) {
      //NEED TO PULL USER DATA?                     

      var user = firebase.auth().currentUser;
      if(user){
        console.log(user.uid);
        $("#popup").click();
      }
    }).catch(function(error) {
   // Handle Errors here.
   var errorCode = error.code;
   var errorMessage = error.message;
   if (errorCode === 'auth/wrong-password') {
     alert('Wrong password.');
   } else {
    alert(errorMessage);
  }
  console.log(error);
});
     }