How to Display Firebase Posts in Descending Posted Order?

How to Display Posts in Descending Posted Order with Firebase

Firebase allows users to post comments using the push method. To display the retrieved data in chronological order, use the following method:

fbl.child('sell').limit(20).on("value", function(fbdata) { 
  // handle data display here
}

However, this code displays the data in order of oldest to newest. To reverse the order, Firebase offers two options:

1. Add an Inverted Timestamp Property: Add a child property with the inverted timestamp (0 - Date.now()) when adding the post.


2. Invert the Data on the Client: Read the children in ascending order using on('child_added') and invert them on the client.

Example Code:

To use the first option, modify the push() code:

var ref = new Firebase('https://your.firebaseio.com/sell');
var item = ref.push();

// Append an inverted timestamp to the post object
var postObject = {...yourObject, timestamp: 0 - Date.now()};

item.setWithPriority(postObject, 0 - Date.now());

To use the second option, modify the retrieval code:

fbl.child('sell').startAt().limitToLast(20).on('child_added', function(fbdata) {
  console.log(fbdata.exportVal());
})

Notes:

• Using on('child_added') ensures that the last few children added are returned in reverse chronological order.
• on('value') returns children in the order of their names.
• Refer to the Firebase documentation on ordered data for more information.

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