how to access a child node firebase nodejs - node.js

Question

hello I have a data like this in my firebase database
I want to access the sender name.
Here is my code
var ref = firebase.database().ref().child('chat');
ref.on("child_added", function(data, prevChildKey) {
var newPlayer = data.val();
var key = data.key;
console.log(key);
});
data.key gives me the key 1-5. I want to access the value for example which is sender_name under 1-5. I don't know how can I do that. I have done something like this
var newPlayer = data.val();
console.log(newPlayer[key]['sender_name'];
But I got an undefined error

Answer 1

Child elements of chat node are 1-5, 6-10, etc. keys, not chat items, based on the data structure you show.
Firebase child_added event is only fired on direct children.
If you wish to listen to new items with child_added listener, you can:
Listen on each chat/1-5, chat/6-10, etc, for added children, but I understand this is not very convenient
Example to always listen to 1-5 children:
var ref = firebase.database().ref().child('chat/1-5');
ref.on("child_added", function(data) {
var item = data.val();
console.log('New message', item['sender_name'], item.text);
});
And a generic solution if you don't know what is the first key but you know it starts with '1-':
var ref = firebase.database().ref().child('chat');
var firstKey = null
ref.on("child_added", function(data) {
// If first key is what you are looking for
// and changed (or is null) update item listener
if (data.key.startsWith('1-') && data.key !== firstKey) {
// But first remove previous listener if present
firstKey && ref.child(firstKey).off("child_added", checkItemsAdded)
firstKey = data.key
ref.child(firstKey).on("child_added", checkItemsAdded)
}
});
function checkItemsAdded(data) {
var item = data.val();
console.log('New message', item['sender_name'], item.text);
}
And even more generic, listen to all intermediary keys (if you don't know what they are):
var ref = firebase.database().ref().child('chat');
ref.on("child_added", function(data) {
// function checkItemsAdded is the same as above
ref.child(firstKey).on("child_added", checkItemsAdded)
});
Note that this code listens to all sub keys like 1-5, etc. So if there are just a few, or a few dozen, I would say it is OK, but I would not advise to scale this above a few hundreds.
Other (recommended) option:
Change data structure in a way that all items are directly written as chat direct children. (Remove 1-5, 6-10 level)

Answer 2

As #Pandaiolo explains, the child_added events fires for direct children of the location you listen to. For each child it gives you a snapshot of all data under that child. So your data parameter contains all the information you're looking for. You just need to loop over it, to get one level deeper into the JSON with:
var ref = firebase.database().ref().child('chat');
ref.on("child_added", function(data, prevChildKey) {
var newPlayer = data.val();
console.log(data.key);
data.forEach(function(child) {
console.log(child.key, child.child("sender_name").val());
});
});
This will print all sender names.