如何从每个 firebase object 中获取最后一项并将其放入数组中

Question

Folks I'm using React Native Firebase and I want to achieve as you can see in the attached ss

there's message key and it has threads underneath and each thread have multiple messages.I want to do like I want get last item from every thread and put it into an array.How to achieve.I'm trying to use foreach and not getting my desired result

here is my code

 messagesRef.on('value', snapshot => {
        let messsagesFB = [];

        snapshot.forEach(element => {
          messsagesFB = [...messsagesFB, element.val()];
        });
      });

I know my code will push every element but i want to push only last item from each thread

Answer 1

For your database reference messagesRef , try adding .orderByKey().limitToLast(1) for the query, in which case a loop would not be needed.

messagesRef.orderByKey().limitToLast(1).on('value', snapshot => {
   // TODO: Add to array
}

There's also always the catch for the last iteration of a jQuery foreach loop. In your case, you could simply do:

snapshot.forEach(function(element, idx, messagesFB) {
   if (idx === messagesFB.length - 1){ 
       messsagesFB.push(element.val());
   }
});