The select function accesses data from specific WordPress stores like core/edit-post for editor state and core/editor for block content. Each store contains different types of application data with dedicated resolvers.
Some data is immediately available (like sidebar state), while other data requires asynchronous database requests (like entity records). Initial calls may return null while the request completes, with subsequent calls returning cached store data.
This asynchronous behavior requires handling loading states in blocks. Components must account for null values during data fetching and show loading indicators until the data becomes available in the store.