firebase increment star count

starBtnClick(value) {
  this.addStar(value)
}

addStar(uid) {
  const myuid = this.state.userId
  firebase.database().ref('/users/' + myuid + '/starred_users/').push().set({
    starUserData: uid
  }).then(function () {
    return firebase.database().ref('users/' + uid + '/starCount').transaction(function(count) {
      count += 1
      return count
    })
  }).then(function (committed) {
    if (committed) {
        // 表示を更新
    }
  })
}