How to retrieve data between two linked endpoints in Firebase

Let's assume that you have the following endpoint in Firebase:

javascript
let lastPosts = {
    'jdJDoljfNmc': {
        'uid': 'JSkssLizO'
    } 
}

Suppose that you have another endpoint such as:

javascript

let users = {
    'JSkssLizO': {
        'posts': {
            'jdJDoljfNmc': {
                'title': 'hello'
                'message': 'hi'
                'timestamp': 1638702647456
            }
        }
    }
}

The uid in lastPosts is linked to the uid in users. If you want to retrieve the data from an endpoint to another:

javascript
import { db, get, onValue, ref } from 'firebase'

onValue(ref(db, `lastPosts/${postId}`), async snapshot => {

    let { uid } = snapshot.val()

    let post = (await get(ref(db, `${uid}/posts/${postId}`))).val()

    // At th is point you have the post info

})

Hi, I'm Erik, an engineer from Barcelona. If you like the post or have any comments, say hi.