Firebase returning undefinfed - firebase

Question

I keep getting a response undefined with the return function. After a second the console.log displays the information. My guess is that the data is still being gathered and that the function is already returning. I thought it would be solved with a promise but it has not. What am I missing? why is my function returning without any data?
TakenSpaces = 0
let startDate = new Date(time)
startDate.setHours(0)
startDate.setMinutes(0)
let endDate = new Date(startDate)
endDate.setHours(24)
data = []
const reservations = db.collection('organisation').doc('Amigos').collection('reservations')
.where('start', '>=', startDate)
.where('start', '<=', endDate).get()
console.log('promse made')
reservations.then((docs) => {
// console.log(docs.data())
// return docs.data()
// const promises = []
docs.forEach((doc) => {
data.push(doc.id)
})
// console.log(data)
// console.log('DONE TESTING')
return data
// return Promise.all(promises)
})
.then((test) => { console.log(test); return test })
// for (const reservation of reservations) {
// console.log(reservation)
// }
// .then((docs) => {
// // for (const doc of docs) {
// // console.log(doc.id)
// // }
// docs.forEach((doc) => {
// if (doc.data().people){
// const people = doc.data().people
// TakenSpaces = TakenSpaces + people
// }
// // console.log(doc.data().people)
// });
// return TakenSpaces
// })
// return TakenSpaces
}
const t = getTakenCapacity(time)
console.log(t)

Answer 1

It works know. But If anyone knows if the function can only return when everything is finished and not have to return a promise function.
function getTakenCapacity (time) {
TakenSpaces = 0
let startDate = new Date(time)
startDate.setHours(0)
startDate.setMinutes(0)
let endDate = new Date(startDate)
endDate.setHours(24)
data = []
const reservations = db.collection('organisation').doc('Amigos').collection('reservations')
.where('start', '>=', startDate)
.where('start', '<=', endDate).get()
return reservations.then((docs) => {
// console.log(docs.data())
// return docs.data()
// const promises = []
var dd = new Array
docs.forEach((doc) => {
data.push([[time], doc.data().people])
})
// console.log(data)
// console.log('DONE TESTING')
return data
// return Promise.all(promises)
})
getTakenCapacity(time).then(function(result) {
console.log(result) // "Some User token"
})