javascript - Firebase更新方法官方示例/push().key作为变量

Question

我注意到该示例使用 .push 方法 but 中的 newPostKey，而不是嵌套在 .then 中且没有回调。在 posted example ， .update 如何知道等待 Promise 解析 newPostKey？ .update 知道变量是一个 promise 吗？换句话说，我像下面这样做。而他们的做法如下:

var postData = {
  "name": supplyNameInput.value,
  "description": supplyDescriptionInput.value,
  "type": doc.querySelector('input[name = "supply-type"]:checked').value,
  "imageURL": clock.now,
  "last modified": clock.now,
  "author": uid
};
var newSupply = suppliesRef.push(postData, function(error) {
  if (error){
    //error
  } else {
    //succesfull
  }
}).then((snap) => {
  suppliesRef.child(snap.key).once('value').then(function(snapshot) {
    // The Promise was fulfilled
    console.log(snap.key);
    //Now I have generated newKey as snap.key
  }, function(error) {
    // The Promise was rejected.
    console.error(error);
  });
});        

官方示例。

function writeNewPost(uid, username, picture, title, body) {
  // A post entry.
  var postData = {
    author: username,
    uid: uid,
    body: body,
    title: title,
    starCount: 0,
    authorPic: picture
  };

  // Get a key for a new Post.
  var newPostKey = firebase.database().ref().child('posts').push().key;

  // Write the new post's data simultaneously in the posts list and the user's post list.
  var updates = {};
  updates['/posts/' + newPostKey] = postData;
  updates['/user-posts/' + uid + '/' + newPostKey] = postData;

  return firebase.database().ref().update(updates);
}

Answer 1

push() 方法(在不带任何参数的情况下调用时，如您从 Firebase 文档中共享的示例中所示)是客户端操作。不需要往返服务器，因为它生成一个在统计上保证在客户端中唯一的 key 。