我一直在使用Firebase Web应用程序，并且在访问数据库的某些元素时突然间，在尝试使用Object.keys以创建一系列键时，它一直抛出一系列异常。迭代每个对象。
这个确切的功能到目前为止工作得很好，数据库的某些子元素仍然没有任何错误。
以下是我遇到问题的代码以及Chrome中引发的错误。任何建议将不胜感激
//reference to firebase database at Flags/Employee t
var ref = database.ref('Flags/Employee');
//Take a snapshot of all Green Flags stored and use as training data for knn
ref.on('value', function(snapshot){
//Array of flag objects
var storedFlags = snapshot.val();
//Array of hashcodes used to access flags
var keys = Object.keys(storedFlags);
//Loop through each flag stored in the database at Flags/Employee
//Find the flags with the smallest distance to the current flag
//Store in a heap for later access
for(var i = 0; i < keys.length; i++){
var currentLookup = storedFlags[keys[i]];
以下是调用Object.keys函数时发生的错误：
firebase-storage.js:3476 Uncaught TypeError: Cannot use 'in' operator to search for 't' in 2
at M (firebase-storage.js:3476)
at t.cr (firebase-storage.js:3476)
at e.onMessage (firebase-storage.js:3476)
at e.nt (firebase-storage.js:3476)
at e.handleIncomingFrame (firebase-storage.js:3476)
at WebSocket.mySock.onmessage (firebase-storage.js:3476)
M @ firebase-storage.js:3476
t.cr @ firebase-storage.js:3476
(anonymous) @ firebase-storage.js:3476
e.nt @ firebase-storage.js:3476
e.handleIncomingFrame @ firebase-storage.js:3476
mySock.onmessage @ firebase-storage.js:3476
VM2298:1 Uncaught SyntaxError: Unexpected end of JSON input
at JSON.parse (<anonymous>)
at r (firebase-storage.js:3476)
at e.nt (firebase-storage.js:3476)
at e.handleIncomingFrame (firebase-storage.js:3476)
at WebSocket.mySock.onmessage (firebase-storage.js:3476)
r @ firebase-storage.js:3476
e.nt @ firebase-storage.js:3476
e.handleIncomingFrame @ firebase-storage.js:3476
mySock.onmessage @ firebase-storage.js:3476
VM2299:1 Uncaught SyntaxError: Unexpected token u in JSON at position 0
at JSON.parse (<anonymous>)
at r (firebase-storage.js:3476)
at e.nt (firebase-storage.js:3476)
at e.handleIncomingFrame (firebase-storage.js:3476)
at WebSocket.mySock.onmessage (firebase-storage.js:3476)
r @ firebase-storage.js:3476
e.nt @ firebase-storage.js:3476
e.handleIncomingFrame @ firebase-storage.js:3476
mySock.onmessage @ firebase-storage.js:3476
recommendations.js:635 null
firebase-storage.js:3476 FIREBASE WARNING: Exception was thrown by user callback. TypeError: Cannot convert undefined or null to object
at Function.keys (<anonymous>)
at file:///home/tyler/Desktop/My%20Websites/DistroRecommendations/recommendations.js:638:24
at t (https://www.gstatic.com/firebasejs/4.3.0/firebase.js:324:64323)
at https://www.gstatic.com/firebasejs/4.3.0/firebase.js:324:59730
at z (https://www.gstatic.com/firebasejs/4.3.0/firebase.js:324:10438)
at t.raise (https://www.gstatic.com/firebasejs/4.3.0/firebase.js:324:110130)
at t.In (https://www.gstatic.com/firebasejs/4.3.0/firebase.js:324:109788)
at t.raiseEventsForChangedPath (https://www.gstatic.com/firebasejs/4.3.0/firebase.js:324:109610)
at Object.onComplete (https://www.gstatic.com/firebasejs/4.3.0/firebase.js:324:140458)
at https://www.gstatic.com/firebasejs/4.3.0/firebase.js:324:129429
R @ firebase-storage.js:3476
(anonymous) @ firebase-storage.js:3476
setTimeout (async)
z @ firebase-storage.js:3476
t.raise @ firebase-storage.js:3476
t.In @ firebase-storage.js:3476
t.raiseEventsForChangedPath @ firebase-storage.js:3476
(anonymous) @ firebase-storage.js:3476
(anonymous) @ firebase-storage.js:3476
e.vr @ firebase-storage.js:3476
t.vr @ firebase-storage.js:3476
t.cr @ firebase-storage.js:3476
(anonymous) @ firebase-storage.js:3476
e.nt @ firebase-storage.js:3476
e.handleIncomingFrame @ firebase-storage.js:3476
mySock.onmessage @ firebase-storage.js:3476
firebase-storage.js:3476 Uncaught TypeError: Cannot convert undefined or null to object
at Function.keys (<anonymous>)
at recommendations.js:638
at t (firebase-storage.js:3476)
at firebase-storage.js:3476
at z (firebase-storage.js:3476)
at t.raise (firebase-storage.js:3476)
at t.In (firebase-storage.js:3476)
at t.raiseEventsForChangedPath (firebase-storage.js:3476)
at Object.onComplete (firebase-storage.js:3476)
at firebase-storage.js:3476