Login - Javascript Chat App

login.js

...
loginBtn.addEventListener('click', function() {
    // show loading indicator.
    showLoading();
    // get input user's credentials.
    const email = emailLoginInputElement ? emailLoginInputElement.value : null;
    const password = passwordLoginInputElement ? passwordLoginInputElement.value : null;
    if(isUserCredentialsValid({email, password})) {
      // if the user's credentials are valid, call Firebase authentication service.
      auth.signInWithEmailAndPassword(email, password).then((userCredential) => {
        const userEmail = userCredential.user.email;
        realTimeDb.ref().child('users').orderByChild('email').equalTo(userEmail).on("value", function(snapshot) {
          const val = snapshot.val();
          if (val) {
            const keys = Object.keys(val);
            const user = val[keys[0]];
            if (user && user.id) {
              CometChatWidget.init({
                "appID": `${config.CometChatAppId}`,
                "appRegion": `${config.CometChatRegion}`,
                "authKey": `${config.CometChatAuthKey}`
              }).then(response => {
                CometChatWidget.login({uid: user.id}).then((loggedInUser) => {
                  // User loged in successfully.
                  // hide loading.
                  hideLoading();
                  // redirect to home page.
                  window.location.href = '/';
                });
              }, error => {
                //Check the reason for error and take appropriate action.
              });
            } else { 
              // hide loading indicator.
              hideLoading();
              alert(`Your user's name or password is not correct`);
            }
          }
        });
      })
      .catch((error) => {      
        // hide loading indicator.
        hideLoading();
        alert(`Your user's name or password is not correct`);
      });
    } else { 
      // hide loading indicator.
      hideLoading();
      alert(`Your user's name or password is not correct`);
    }
  });
...