Return promise if data is available or not? Firebase-Angular

Question

I need to know whether this data entry is available or not. So I need to handle promise to return boolean. I tried various ways but it didn't work. I use the below code to do the task, I need to return promise as boolean.

 //constants for the database data lists
    readonly USER_CHILD_ROOT: string = "user";

    list: AngularFireList<any>;

    private newUser: DatabaseUser = {
        uid: "",
        email: "",
        name: "",
        address01: "",
        address02: "",
        address03: "",
        telephone: "",
    }
    fileList: any[];
    constructor(@Inject(AngularFireDatabase) private firebase: AngularFireDatabase) { }

    isUserAvailable(userEmail: string): boolean {
        var output: boolean = false;
        this.firebase.list(this.USER_CHILD_ROOT)
            .snapshotChanges()
            .subscribe(
                list => {
                    this.fileList = list.map(item => { return item.payload.key; });
                    this.fileList.forEach(element => {
                        if (element === userEmail)
                            output = true;
                        //console.log(element);
                    });
                });
        return output;
    }

Answer 1

This modified solution worked.

async isUserAvailable(userEmail: string) {

            return await new Promise(resolve => {
                this.firebase.list(this.USER_CHILD_ROOT)
                    .snapshotChanges()
                    .subscribe(
                        list => {
                            this.fileList = list.map(item => { return item.payload.key; });
                            this.fileList.forEach(element => {
                                if (element === userEmail) {
                                    resolve(true);
                                } else {
                                    resolve(false);
                                }
                            });
                        });
            });
        }

Call and wait for the response.

let promise = this.fdd.isUserAvailable("user email");
   promise.then(
    function(result){
    if(result)console.log("found!")
    }
   );