firestore create document with auto id
// Add a new document with a generated id.
db.collection("cities").add({
name: "Tokyo",
country: "Japan"
})
.then(function(docRef) {
console.log("Document written with ID: ", docRef.id);
})
.catch(function(error) {
console.error("Error adding document: ", error);
});
---------------------------
//If you want to specify id then use .set()
// e.x /
db.collection("cities").doc("TYO").set({
name: "Tokyo",
country: "Japan"
})