Firebase returns undefined when it comes to snapshot.val()

Question

I use NextJS

  const db = getDatabase()

  const getTeamData = (teamName: string) => {
    onValue(ref(db, teamName), snapshot => {
      return snapshot.val()
    })
  }
 
  console.log(getTeamData('exampleTeam'))

I do have this exampleTeam in the database; however, it returns undefined anyway. But why?

I have tried this:

    let ret: any[] = []
    onValue(ref(db, teamName), snapshot => {
      ret.push(snapshot.val())
    })
    return ret[0]
  }

But it still returns undefined.

Also, if I change something in the code so that it does a fast reload, then all of the correct data is printed and it works good.