Function onSnapshot

onSnapshot<T>(nodeOrFn, listener): OnSnapshotDisposer
Adds a reaction that will trigger every time an snapshot changes.
Type Parameters
- T extends object
Parameters
- nodeOrFn: T | (() => T)
  Object to get the snapshot from or a function to get it.
- listener: OnSnapshotListener<T>
  Function that will be triggered when the snapshot changes.
Returns OnSnapshotDisposer
A disposer.

Typeparam
T Object type.