firestore query pagination

big_collection.js

let sum = 0;
let last = null
let snapshot = null
while (true) {
    if (last) {
        snapshot = await db.collection('count').where('amount', '>', 0).select('amount').limit(1000).startAfter(last).get()
    } else {
        snapshot = await db.collection('count').where('amount', '>', 0).select('amount').limit(1000).get()
    }
    snapshot.forEach(doc => {
        sum += doc.data()['amount']
    })
    let len = snapshot.docs.length;
    if (len < 1000) {
        break
    } else {
        last = snapshot.docs[snapshot.docs.length - 1];
    }
}

console.log({sum})

small_collection.js

let sum = 0;
snapshot = await db.collection('count').where('amount', '>', 0).select('amount').get()
snapshot.forEach(doc => {
    sum += doc.data()['amount']
})
console.log({sum})