facebook.js

// These samples are intended for Web so this import would normally be
// done in HTML however using modules here is more convenient for
// ensuring sample correctness offline.
import firebase from "firebase/app";
import "firebase/auth";

function facebookProvider() {
  // [START auth_facebook_provider_create]
  var provider = new firebase.auth.FacebookAuthProvider();
  // [END auth_facebook_provider_create]

  // / [START auth_facebook_provider_scopes]
  provider.addScope('user_birthday');
  // [END auth_facebook_provider_scopes]

  // [START auth_facebook_provider_params]
  provider.setCustomParameters({
    'display': 'popup'
  });
  // [END auth_facebook_provider_params]
}

function facebookSignInPopup(provider) {
  // [START auth_facebook_signin_popup]
  firebase
    .auth()
    .signInWithPopup(provider)
    .then((result) => {
      /** @type {firebase.auth.OAuthCredential} */
      var credential = result.credential;

      // The signed-in user info.
      var user = result.user;
      // IdP data available in result.additionalUserInfo.profile.
        // ...

      // This gives you a Facebook Access Token. You can use it to access the Facebook API.
      var accessToken = credential.accessToken;

      // ...
    })
    .catch((error) => {
      // Handle Errors here.
      var errorCode = error.code;
      var errorMessage = error.message;
      // The email of the user's account used.
      var email = error.email;
      // The firebase.auth.AuthCredential type that was used.
      var credential = error.credential;

      // ...
    });
  // [END auth_facebook_signin_popup]
}

function facebookSignInRedirectResult() {
  // [START auth_facebook_signin_redirect_result]
  firebase.auth()
    .getRedirectResult()
    .then((result) => {
      if (result.credential) {
        /** @type {firebase.auth.OAuthCredential} */
        var credential = result.credential;

        // This gives you a Facebook Access Token. You can use it to access the Facebook API.
        var token = credential.accessToken;
        // ...
      }
      // The signed-in user info.
      var user = result.user;
      // IdP data available in result.additionalUserInfo.profile.
        // ...
    }).catch((error) => {
      // Handle Errors here.
      var errorCode = error.code;
      var errorMessage = error.message;
      // The email of the user's account used.
      var email = error.email;
      // The firebase.auth.AuthCredential type that was used.
      var credential = error.credential;
      // ...
    });
  // [END auth_facebook_signin_redirect_result]
}

// [START auth_facebook_callback]
function checkLoginState(response) {
  if (response.authResponse) {
    // User is signed-in Facebook.
    var unsubscribe = firebase.auth().onAuthStateChanged((firebaseUser) => {
      unsubscribe();
      // Check if we are already signed-in Firebase with the correct user.
      if (!isUserEqual(response.authResponse, firebaseUser)) {
        // Build Firebase credential with the Facebook auth token.
        var credential = firebase.auth.FacebookAuthProvider.credential(
            response.authResponse.accessToken);
        
        // Sign in with the credential from the Facebook user.
        firebase.auth().signInWithCredential(credential)
          .catch((error) => {
            // Handle Errors here.
            var errorCode = error.code;
            var errorMessage = error.message;
            // The email of the user's account used.
            var email = error.email;
            // The firebase.auth.AuthCredential type that was used.
            var credential = error.credential;
            // ...
          });
      } else {
        // User is already signed-in Firebase with the correct user.
      }
    });
  } else {
    // User is signed-out of Facebook.
    firebase.auth().signOut();
  }
}
// [END auth_facebook_callback]

// [START auth_facebook_checksameuser]
function isUserEqual(facebookAuthResponse, firebaseUser) {
  if (firebaseUser) {
    var providerData = firebaseUser.providerData;
    for (var i = 0; i < providerData.length; i++) {
      if (providerData[i].providerId === firebase.auth.FacebookAuthProvider.PROVIDER_ID &&
          providerData[i].uid === facebookAuthResponse.userID) {
        // We don't need to re-auth the Firebase connection.
        return true;
      }
    }
  }
  return false;
}
// [END auth_facebook_checksameuser]

function authWithCredential(credential) {
  // [START auth_facebook_signin_credential]
  // Sign in with the credential from the Facebook user.
  firebase.auth().signInWithCredential(credential)
    .then((result) => {
      // Signed in       
      var credential = result.credential;
      // ...
    })
    .catch((error) => {
      // Handle Errors here.
      var errorCode = error.code;
      var errorMessage = error.message;
      // The email of the user's account used.
      var email = error.email;
      // The firebase.auth.AuthCredential type that was used.
      var credential = error.credential;
      // ...
    });
  // [END auth_facebook_signin_credential]
}

function facebookProviderCredential(accessToken) {
  // [START auth_facebook_provider_credential]
  var credential = firebase.auth.FacebookAuthProvider.credential(accessToken);
  // [END auth_facebook_provider_credential]
}