want to have docChanges on onQuery etc.

[reedom]

For the client side performance improvement, I want to have "docChanges" on "onQuery" and other "on" series. https://firebase.google.com/docs/firestore/query-data/listen#view_changes_between_snapshots

To achieve it, I think there are several API candidates while the docChanges should be supplied optionally for performance reasons.

1. Introduce variant functions for each "on" series. E.g. onQueryWithDocChanges for onQuery

   export default function onQueryWithDocChanges<Model>(
   collection: Collection<Model> | CollectionGroup<Model>,
   queries: Query<Model, keyof Model>[],
   onResult: (docs: Doc<Model>[], docChanges: DocChange<Model>[]),
   onError?: (err: Error) => any
   ): () => void {

2. Add an options specification argument to let clients specify their requirement

   export default function onQuery<Model>(
   collection: Collection<Model> | CollectionGroup<Model>,
   queries: Query<Model, keyof Model>[],
   onResult: (docs: Doc<Model>[], extra?: { docChanges?: DocChange<Model>[] }),
   onError?: (err: Error) => any,
   options?: { docChanges?: boolean }
   ): () => void {

3. Add an "getter" to onResult's argument

   export default function onQuery<Model>(
   collection: Collection<Model> | CollectionGroup<Model>,
   queries: Query<Model, keyof Model>[],
   onResult: (docs: Doc<Model>[], getDocChanges: () => DocChange<Model>[]) => any,
   onError?: (err: Error) => any
   ): () => void {

A sample implementation to the 3rd. https://github.com/kossnocorp/typesaurus/compare/master...reedom:feature/docchanges?expand=1 But as reviewing Firebase.QuerySnapshot now again, chances are that someone might want to get readTime. So, the 2nd would be better while it's expandable.

[kossnocorp]

I love it, and I agree that the 2nd option works the best. I will happily accept a pull-request and help if it would be needed.