async function getMessagesOfAllUsers(userlist){
    let outstate = false, data = {};
    if (userlist !== null)
        for (let i = userlist.length - 1; i >= 0; i--) {
            outstate = await this.getMessagesOfOneUsers(userlist[i].user);
            if (outstate !== false) data = { ...data, ...outstate };
            if (i === 0) {
                this.setState({ ...this.state, ...data });
            }
        }
}

function getMessagesOfOneUsers(user) {
    return db.collection('users/'+user/+'/messages').orderBy("dt", "desc").limit(10).get().then(snap => {
        let l = snap.size;
        if (l > 0) {
            const ourMessage = this.state.me + user;
            this.lastVisible = { ...this.lastVisible, ...{ [user]: snap.docs[l - 1] } };
            for (let i = 0; i < l; i++) {
                if (this.outState[ourMessage] !== undefined)
                    this.outState[ourMessage] = [...this.outState[ourMessage], snap.docs[i].data()];
                else this.outState[ourMessage] = [snap.docs[i].data()];
                if (i === l - 1) return this.outState;
            }
        }
        return false;
    });
}