How i can get value from database

Question

i need to get online status of user here's function where i listen online status

onlineStatus(id) {
 app.database().ref('users').child(id).child('connections').on('value', (snapshot) => {
 return snapshot.val();
 })
 }

but when i try to use this function in return function i get undefined value

{this.state.diologs.map(i =>
 this.state.searchResult.length === 0 && this.state.isDiologOpen === false &&
 <div className="resultField" >
 <img src="/images/noavatar.png" id="userImage" />
 <p className="userName">{i.name} {i.surname} </p>
 <p>{i.lastMessage}</p>
 <button onClick={() => this.writeMessage(i)}>Написать сообщение</button>
 {this.onlineStatus(i.id) ? <p>Online</p> : <p>Offline</p>}

the problem is in this line

{this.onlineStatus(i.id) ? <p>Online</p> : <p>Offline</p>}

• Doug Stevenson: Use once() instead of on() to query a single time and return a promise to the caller with the data from the query.
• Toan Quoc Ho: It shows undefined because onlineStatus doesn't return any data. The return statement inside onlineStatus currently just return for the callback instead of the method. I don't have enough information about the context of your problem but seems like your approach is not effective and even not doable. React rendering doesn't work that way.