Data is loaded from Firestore (and from most modern web APIs) asynchronously. This means that the rest of your code continues to execute after you start the query, and then when the data comes back from the database, your then() callback is called. This in turn means that all code that needs access to the data from the database, must be inside the then() callback.
db.collection("checkout")
.get()
.then(querySnapshot => {
querySnapshot.forEach(doc => {
const data = {
id: doc.id, // firebase document id
book_did: doc.data().book_did,
borrowed_date: doc.data().borrowed_date,
copies_did: doc.data().copies_did,
due_date: doc.data().due_date
};
this.checkout.push(data); // push to array
console.log(this.checkout) // show data, as in the image below
console.log(this.checkout.length) // get 0
console.log(Object.keys(this.checkout).length) // get 0
});
});
}
......
Also see:
