javascript - Handling linking accounts in Firebase -

i following firebase's instruction on social login. below example of using , working fine login authentication perspective.

i have, however, both google , facebook login working independently.

what able link accounts. can see below in fact might go (see comment):

if using multiple auth providers on app should handle linking user's accounts here.

i have tried many variations of think should go here, no avail. can guide me in relation think should go here? thanks!

function initfbapp() {     // result redirect auth flow.     // [start getidptoken]     firebase.auth().getredirectresult().then(function (result) {         if (result.credential) {             // gives facebook access token. can use access facebook api.             var token = result.credential.accesstoken;             // [start_exclude]             document.getelementbyid('fbquickstart-oauthtoken').textcontent = token;         }         else {             document.getelementbyid('fbquickstart-oauthtoken').textcontent = 'null';             // [end_exclude]         }         // signed-in user info.         var user = result.user;     }).catch(function (error) {         // handle errors here.         var errorcode = error.code;         var errormessage = error.message;         // email of user's account used.         var email = error.email;         // firebase.auth.authcredential type used.         var credential = error.credential;         // [start_exclude]         if (errorcode === 'auth/account-exists-with-different-credential') {             alert('you have signed different auth provider emails.');             // if using multiple auth providers on app should handle linking             // user's accounts here.         }         else {             console.error(error);         }         // [end_exclude]     });     // [end getidptoken]     // listening auth state changes.     // [start authstatelistener]     firebase.auth().onauthstatechanged(function (user) {         if (user) {             // user signed in.             var displayname = user.displayname;             var email = user.email;             var emailverified = user.emailverified;             var photourl = user.photourl;             var isanonymous = user.isanonymous;             var uid = user.uid;             var providerdata = user.providerdata;             // [start_exclude]             document.getelementbyid('fbquickstart-sign-in-status').textcontent = 'signed in';             document.getelementbyid('fbquickstart-sign-in').textcontent = 'log out';             document.getelementbyid('fbquickstart-account-details').textcontent = json.stringify(user, null, '  ');             // [end_exclude]         }         else {             // user signed out.             // [start_exclude]             document.getelementbyid('fbquickstart-sign-in-status').textcontent = 'signed out';             document.getelementbyid('fbquickstart-sign-in').textcontent = 'log in facebook';             document.getelementbyid('fbquickstart-account-details').textcontent = 'null';             document.getelementbyid('fbquickstart-oauthtoken').textcontent = 'null';             // [end_exclude]         }         // [start_exclude]         document.getelementbyid('fbquickstart-sign-in').disabled = false;         // [end_exclude]     });     // [end authstatelistener]     document.getelementbyid('fbquickstart-sign-in').addeventlistener('click', togglefbsignin, false); } 

these steps on how handle auth/account-exists-with-different-credential: error if signing in new facebook account uses email of account exists. let's existing account google account.

you error in getredirectresult().catch(function(error) {})

the error contain email , credential field. need save credential (using recommended sessionstorage). check post more on that: firebase authentication javascript: setcookie pending credential redirect

you call firebase.auth().fetchprovidersforemail(error.email) determine providers exist email.

you sign in 1 of existing providers , assert email same error.email. on success, load pending credential sessionstorage, re-initialize described in other post , link currentuser:

firebase.auth().currentuser.link(savedcred); 

you have both accounts linked. keep in mind existing provider password type. in case don't need save credential, ask user password , sign them in using same email error.email. can call link directly error.credential.

btw, recommend firebaseui-web takes care of you: https://github.com/firebase/firebaseui-web