Exception was thrown by user callback. TypeError: Cannot add property 0, object is not extensible
at Array.push (<anonymous>)
at blob:file:///d0f11e65-c690-4662-8ef6-91001f662c11:104234:59
at blob:file:///d0f11e65-c690-4662-8ef6-91001f662c11:90326:24
at LLRBNode.inorderTraversal (blob:file:///d0f11e65-c690-4662-8ef6-91001f662c11:89149:58)
at SortedMap.inorderTraversal (blob:file:///d0f11e65-c690-4662-8ef6-91001f662c11:89453:31)
at ChildrenNode.forEachChild (blob:file:///d0f11e65-c690-4662-8ef6-91001f662c11:89926:39)
at DataSnapshot.forEach (blob:file:///d0f11e65-c690-4662-8ef6-91001f662c11:90325:35)
at blob:file:///d0f11e65-c690-4662-8ef6-91001f662c11:104233:35
at onceCallback (blob:file:///d0f11e65-c690-4662-8ef6-91001f662c11:90716:55)
at blob:file:///d0f11e65-c690-4662-8ef6-91001f662c11:90450:26

ExceptionsManager.js:63 Cannot add property 0, object is not extensible

authLoggedInUserKey = userKey;
                let requestedUser = [];
                //This code get data form the user to whom loggedin user send request
                let userDetail = userRef.child(authLoggedInUserKey).child('requestedUserData');
                userDetail.once('value',(snap) =>{
                    snap.forEach((child) => {
                        let requestedUserKey = child.val().requestedUser;
                        let requestedUserDetail = userRef.orderByKey().equalTo(requestedUserKey);
                        requestedUserDetail.once('value',(snap1)=>{
                            snap1.forEach((child1) => {

                                requestedUser.push({ //Error generated here
                                    firstName: child1.val().firstName,

                                })

                            })

                        })
                    })

snap1.forEach((child1) => {

                            requestedUser.push({ //Error generated here
                                firstName: child1.val().firstName,

                            })
                            Object.preventExtensions(requestedUser)


                        })