var collection = {    "5439": {      "album": "ABBA Gold"    }};function updateRecords(id, prop, value) {  if(prop !== "tracks" && value !== ""){    collection[id].prop=value;  }  return collection;}updateRecords(5439, "artist", "ABBA");為何結果是    Object { album="ABBA Gold",  prop="ABBA"}      不是  Object { album="ABBA Gold",artist="ABBA"}      ？在運行到這里的時候   collection[id].prop=value; prop的值artist，因該會代入，id的值5439也代入形成collection[id].prop=value;因該是 collection[9439].artist="ABBA";