我試圖了解 Firebase 中的查詢。我想傳遞 userId A 和 B，看看他們是否訂閱了一個共同的 chatId，它會返回 true 或 false。如何查詢 userId 并評估我想要的輸出的結果？export const checkForExistingChat = (currentUserId, recipient) => {  var IdList = {}  var query = database    .ref(`Chats/${currentUserId}`)    .orderByChild("subscribedToChat")    .once("value", function (dataSnapshot) {      dataSnapshot.forEach(function (childSnapshot) {        const childData = childSnapshot.val();        console.log("childData : ", childData);      });    });};導出聊天的 JSON  "Chats" : {    "61vtPjp8YVVSzpvexwXMgEHghYf1" : {      "subscribedToChat" : {        "1a555cbf-30b7-4c8f-9986-4252a7620c45" : "1a555cbf-30b7-4c8f-9986-4252a7620c45",        "2d718ea7-eafa-48db-af14-f165f07b3b08" : "2d718ea7-eafa-48db-af14-f165f07b3b08",        "2e4fd8bb-4afb-4229-83ec-5a427fe2731d" : "2e4fd8bb-4afb-4229-83ec-5a427fe2731d",        "35c537ef-57dd-48c5-9350-5d1fe2e9d118" : "35c537ef-57dd-48c5-9350-5d1fe2e9d118",        "3a816ac1-6e97-4d66-ae19-77e65f8c2df4" : "3a816ac1-6e97-4d66-ae19-77e65f8c2df4",        }    },    "qqpBNbEa8ZSiCEUlseFeGeiRqzh2" : {      "subscribedToChat" : {        "1a555cbf-30b7-4c8f-9986-4252a7620c45" : "1a555cbf-30b7-4c8f-9986-4252a7620c45",        "35c537ef-57dd-48c5-9350-5d1fe2e9d118" : "35c537ef-57dd-48c5-9350-5d1fe2e9d118"      }    }  }