对于发现此问题并使用的任何人Firebase 3+，推送后获取自动生成的对象唯一 ID 的方法是使用Promise快照上的key属性（而不是方法）：

firebase
  .ref('item')
  .push({...})
  .then((snap) => {
     const key = snap.key 
  })

在Firebase 文档中阅读更多相关信息。

附带说明一下，那些考虑生成自己的唯一 ID 的人应该三思而后行。它可能具有安全性和性能影响。如果您不确定，请使用 Firebase 的 ID。它包含一个时间戳，并具有一些开箱即用的简洁安全功能。

更多关于它的信息：

push() 生成的唯一键按当前时间排序，因此生成的项目列表将按时间顺序排序。密钥也被设计为不可猜测的（它们包含 72 个随机位的熵）。

要获取任何快照的“名称”（在这种情况下，由 push() 创建的 ID）只需像这样调用 name() ：

var name = snapshot.name();

如果你想获取由 push() 自动生成的名称，你可以在返回的引用上调用 name() ，如下所示：

var newRef = myDataRef.push(...);
var newID = newRef.name();

注意： snapshot.name()已被弃用。查看其他答案。

snapshot.name()已被弃用。使用key来代替。key任何 DataSnapshot 上的属性（代表 Firebase 根的除外）将返回生成它的位置的键名。在你的例子中：

myDataRef.on('child_added', function(snapshot) {
    var message = snapshot.val();
    var id = snapshot.key;
    displayChatMessage(message.name, message.text, message.category, message.enabled, message.approved);
});

要获得成功uniqueID，push()您必须使用此变体：

// Generate a reference to a new location and add some data using push()
 var newPostRef = postsRef.push();
// Get the unique key generated by push()
var postId = newPostRef.key;

Ref当你push()使用.key这个 ref时你会生成一个新的，你可以获得uniqueID.

正如@Rima 指出的那样，key()是获取分配给您的push().

但是，如果您希望去掉中间人，Firebase 发布了带有 ID 生成代码的要点。它只是当前时间的函数，这就是它们如何保证唯一性，即使没有与服务器通信。

有了它，您可以使用generateId(obj)并set(obj)复制push()

这是 ID 函数：

/**
 * Fancy ID generator that creates 20-character string identifiers with the following properties:
 *
 * 1. They're based on timestamp so that they sort *after* any existing ids.
 * 2. They contain 72-bits of random data after the timestamp so that IDs won't collide with other clients' IDs.
 * 3. They sort *lexicographically* (so the timestamp is converted to characters that will sort properly).
 * 4. They're monotonically increasing.  Even if you generate more than one in the same timestamp, the
 *    latter ones will sort after the former ones.  We do this by using the previous random bits
 *    but "incrementing" them by 1 (only in the case of a timestamp collision).
 */
generatePushID = (function() {
  // Modeled after base64 web-safe chars, but ordered by ASCII.
  var PUSH_CHARS = '-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz';

  // Timestamp of last push, used to prevent local collisions if you push twice in one ms.
  var lastPushTime = 0;

  // We generate 72-bits of randomness which get turned into 12 characters and appended to the
  // timestamp to prevent collisions with other clients.  We store the last characters we
  // generated because in the event of a collision, we'll use those same characters except
  // "incremented" by one.
  var lastRandChars = [];

  return function() {
    var now = new Date().getTime();
    var duplicateTime = (now === lastPushTime);
    lastPushTime = now;

    var timeStampChars = new Array(8);
    for (var i = 7; i >= 0; i--) {
      timeStampChars[i] = PUSH_CHARS.charAt(now % 64);
      // NOTE: Can't use << here because javascript will convert to int and lose the upper bits.
      now = Math.floor(now / 64);
    }
    if (now !== 0) throw new Error('We should have converted the entire timestamp.');

    var id = timeStampChars.join('');

    if (!duplicateTime) {
      for (i = 0; i < 12; i++) {
        lastRandChars[i] = Math.floor(Math.random() * 64);
      }
    } else {
      // If the timestamp hasn't changed since last push, use the same random number, except incremented by 1.
      for (i = 11; i >= 0 && lastRandChars[i] === 63; i--) {
        lastRandChars[i] = 0;
      }
      lastRandChars[i]++;
    }
    for (i = 0; i < 12; i++) {
      id += PUSH_CHARS.charAt(lastRandChars[i]);
    }
    if(id.length != 20) throw new Error('Length should be 20.');

    return id;
  };
})();